Help..I am becoming concerned for my newborn's safety.
You've got a baby and a toddler. So, in short, yes, you're doing the right thing in terms of teaching her to be gentle and not expecting her to understand the harm she could do. The thing that I would add is that until your infant gets to be old enough and strong enough to defend herself, one or the other has to be with you. You cannot leave the 26 month old alone with the little sister. She just doesn't have the impulse control.
The other thing I'd add is that she may be doing it for a variety of reasons, not just because she's feeling left out. She may be genuinely curious about what happens. She may be seeking attention, and has discovered that she gets a lot of attention really fast when she does it. (No matter how much attention you give her, most children want more, even as only children. So this may not be feeling left out.) If you can prevent access to her little sister, you'll remove the possibility of experimenting and attention-getting.
Hugs, mama! I know how hard this is. My girls are also 26 mo. apart. DD1 did great with DD2 for the first couple weeks, then all of a sudden she was doing the same things you describe. First of all, know that this will pass and your primary goal is to keep the baby safe. Yes, you need to teach DD1 how to act (gentle touches, etc.), but for awhile you're just going to make sure that they are NEVER alone and avoid contact as much as possible.
What I did was set up a pack n play for DD1 to go into when she was showing any aggressive behaviors. This wasn't really used as a punishment, and I put it right in the main living area, but more as a way to separate them. I probably only had to use it for a couple weeks until things settled down. I definitely put her there when I was nursing the baby because she always hit her while we were sitting down.
The other thing I did was to stop DD1 before she came within a few feet of DD2 and ask her to tell me what she was going to do. Sometimes she would flat out say "I'm going to hit her", so obviously I avoided contact. I told her that until she can show loving behaviors that she can't be close to the baby.
At first I was "afraid" of making them separate, etc. because I wanted them to love each other and be so close, and I felt bad telling DD1 that she can't come by her. Then I started looking at it like a priveledge to be close to the baby and to earn that she needed to show that she could behave appropriately. A 2 yr old can seriously injure a baby and that was no risk I was willing to take.
So in my mind when it comes to safety, just talking and explaining gentle touches, etc. is not the right approach. Physical separation until she can show that she can be loving was the only way that I felt comfortable.
I was so worried about this too, and I would say that our rough period lasted maybe a month total. Now they're 3.5 and 14 mo. and we have a whole new set of challenges, but things are SO much better and they truly do love each other so much.
Hang in there, and make sure to give DD1 as much quality time with you as possible when someone can watch the baby or she's sleeping.
It gets much better, good luck!
I think you might be giving her too much attention after she has been rough with the baby. I know most people on here are anti "time outs", but I think this would one time I would use them.
Then, first thing every day, or after a nap, or when ODD is in a great mood I would spend some time with her, talking to her about baby sister and how to use gentle loving touches. When she DOES use gentle loving touches, react in a super overly dramatic proud happy way. When she is rough, gently remove her from the situation, put her somewhere safe but away from baby and you, and say, "When you're rough with the baby you may not be near her". If she throws a tantrum fine. Get her after a minute or 2 and give her hugs and tell her you love her, and ask her to say sorry to the baby.
She should get the picture pretty quickly.
Congrats on your little one! My oldest two have pretty much the same age difference, 27 months. She did exhibit very similar behaviours when DS was a few weeks old, and at first I was doing pretty much what you are doing. "Gentle hands," "gentle with the baby," gently removing her from the situation and talking to her about it. It didn't help. I've posted this story a gazzillion times here, but I will share it again. Right at that time 'Hold on to your Kids' by Gordon Neufeld arrived and I was eager to read it, hoping for advice and solutions.
Neufeld recommends "collecting before correcting." Meaning that when a child is upset or on a different wave length from you, he is not really in the receptive mood and a correction won't get through. He also states that children are different from lab rats, in the way that they don't need an IMMEDIATE correction after an undesirable action. They DO know they've done wrong. So the next time DD tried to shake DS, I grabbed her on my lap and cuddle with her. I said nothing about what she was doing to DS. I offered to read a book together. When she relaxed in my arms, I told her yet again about gentle hands and not hurting her brother. And it worked! Within a day or two, the behaviour stopped.
Another great advice that worked was from Easy to Love, Difficult to Discipline by Becky Bailey. She suggests you validate the feeling, but don't necessarily accept the manifestation. In this case, the feeling is simple and valid. You could say, "You wish you had mommy's attention now. You wish we could do X or Y together, and we can't. That's okay to want it, but hurting your brother is not okay."
And one other thing--our first borns will always seem a bit older to us, than they actually are. I remember how 'big' and 'grown up' DD looked to me when DS was born. Now, DD2 is 3 year sold, and she still seems like a baby to me! I try to remember that, when I think that DD1 "should know better."
I applaud your tenacity for talking it out with your older child, but at 26 months (I have one the same age and a 6 week old) you sound like the teacher from Peanuts comics. Too many words. When dd2 does stuff such as this to my youngest, ds2, she is told, "no". Period. Plain. & Simple. Then she is moved, physically picked up by me and moved. I also make sure that when I leave the room and baby is there, in a swing, on the floor, etc. I take her with me and give her a job. Even if it is to pick up something I chuck down the hall to give her something to do. Then she is busy. She is also my 'helper mama' we make a big deal of her having to help with baby stuff. She has her babies that we keep everywhere and I have her do lots of the same things with her baby that I am doing with ds2.
Lot so distractions. Coloring, singing, songs on the ipod. We are at the park lots and lots too. Even today when it was 107 degrees outside we were at the park for about 3 hours and dd2 was run ragged, she played in the splashpad and made new friends and had lunch and ran around the park to tire her out.