You don't have any control over her behavior, but you have total control over your reaction to it. There's really no reason why anything she's says *must* hurt your feelings, make you angry, or effect the way you feel at all. Part of the problem is that you are jumping into her unbalanced state with her, giving her control over your emotions.
When her lack of self control starts getting to you, find a way for the two of you to be in separate spaces. Rather than demanding something from her (which she isn't capable of right now) disengage. Take a few minutes to yourself (do a little deep breathing, color a mandela, surf the net, etc.) or if you have things you need to do in the main part of the house, nicely say that you guys needs break from each other, but that you will be working in the kitchen, and politely ask her to be in a different part of the house. "We need to NOT be in the same part of the house for a little while" may be the most helpful thing she can hear from you.
The result of "letting things go" was I ignored her attitude issues, which is hardly fair to my other children, and everyone walked on eggshells for fear of setting her off.
... This is a child who has been much loved, respected, listenned to and treated generously since birth, and in the last 6 months/year has turned into someone who is extremely difficult to live with and is borderline toxic in this house.
"Walking on eggshells in fear" and "letting things go" aren't the same thing. It's really OK if she loses it. That's just where she is right now. She may need more time alone that she used to. She may need some space to be grumpy. Every example that you've given is about how her behavior effected *you* not your other kids, and how much you let this get to you (or not) is totally up to you.
I totally relate to the "much loved, respected, listened to, and treated generously" thing, and I know several other parents on here do too. These are kids who were breastfeed, co-slept, experienced only gentle discipline, etc. Yet they still get hormones! It really isn't fair. But we did all those things because they were the right thing to do, because they felt right in our hearts. Not because they came with a money back guarantee that our kids would always be pleasant and never go through any icky stages.