I have a strong-willed 2.5yo who hits and a possessive 3.5yo who bites right now and I'm expecting sometime in the middle of April. My DH won't have more than a day or two off for the birth and will be out of the country in mid-May. My family lives on the other side of the US from us and we don't have many friends who would understand-- we overwhelmingly know single, childless types. So...I completely understand what you're saying.
I think it's important to identify a way you're willing to slack off PP. It's different for everybody: some people cannot do dirty kitchens but are happy to let their smalls watch TV, some people need to stick to their homeschooling rhythm but are cool with getting to know the pizza delivery driver really well, some people must abide by their food resolutions but gladly skip housework for a couple of weeks. Think about where that give is for you and get comfortable with the idea of falling back on that.
I'd also like to echo the prep work thing. I have been socking away some baked goods and soups in small serving sizes in our freezer (and no, we don't have a full freezer, I just found room anyway), and I've hidden a flat of last summer's canning under my dresser to reserve it. BUT, I have also researched the pre-made food options at our local stores and checked ingredients and made a list of things we can just pick up (some of my favorite things in that category are Amy's burritos). Last time, we only had one meal brought to us, and the family who brought it moved out of state last year, so food is a big one for me.
Prep work also applies to cleaning! If you are one of those people who gets deep-clean-everything urges during pregnancy, GO WITH IT. The purpose of nesting is to prepare your nest! If your house can be really frighteningly clean a week or two before baby arrives, it won't get really nasty, even if you scale way back to minimal housework, for two weeks or better after you give birth. And, since your DD is older, housework is a great thing for her to help with-- my smalls competently wipe walls, clean windows, wash laundry (with a bit of help, since they aren't really good about keeping water in the washtub), clean the bathtub, scour the sink, wash the dishes, put away laundry, polish furniture, pick up their things...I just make sure they have access to safe supplies and check their work afterward. They have a great time doing it, and it keeps them out of trouble (um...relatively), AND things get cleaned! You still have time to get your DD involved if you want to.
Childcare is a big one. You can ask around and see if somebody has a responsible child of 10-13 who could help you out for a couple of hours a couple times per week. Junior babysitters are super-helpful, because while they cost less than a full babysitter, they help you fill in the gaps in your life. I personally find it more helpful than full babysitting, because I can be right there to answer questions and step in if things get too wild, but I can rely on being able to finish my baking or getting a chance to sit down at my sewing machine. You can't go see a movie or anything, but you could have someone to run around in the yard with your DD while you nurse the baby, or keep an eye on things while you take a shower, or bring you tea*. My smalls are happy to watch Netflix for a while (we highly recommend Ruby Gloom, if anybody is looking for a place to start for solid entertainment and non-appalling social norms), but having a tween come by on Wednesday after school saved me last time and I'm sure it will make a world of difference this time, too.
Oh wow, I'm really ramble-y today. I hope I said at least a couple of useful things somewhere in there...good luck, OP!
*Specifically about the tea, we have an insulated carafe (I want to say it's Trudeau brand?) that keeps tea hot all day. I make a pot in the morning, pour it in there, and still have too-hot-to-drink-right-away tea at 2pm. It rocks my socks.