The hormone trip is something else. She probably feels out of control because she really can't control the mood swings and everything. Plus, parenthood is scary, because you don't know what your kids will be like, or if you'll like them, or if you'll be able to handle it, and you have all sorts of fears. And twins makes it even worse, because you'll be twice as tired, and it will be twice the financial burden. One new baby is difficult enough! So, to some extent the irritability is normal, but because she's going to be a single mother, the stress is infinitely greater. You may need to urge her to discuss this with her physician, and find a support group. Make sure she talks with people in the community, like friends with kids, church friends, etc., to get to know people she can call on for help when the kids come. She will need someone to help with the feedings, to watch the kids so she can sleep, to get help when she needs groceries or diapers (www.diapers.com is a great site - she can have ANYTHING baby delivered to her door!), or just to talk to someone or cry on their shoulder. She won't be going out of the house for the first month at least, while the babies are young and she is exhausted. Plus they're highly susceptible to illness, so she'll be staying secluded to avoid exposing the kids to infection. The babies can't be expected to sleep more than 3 hours in a row at any point until about 4 months of age, so she's really going to need a lot of help for at least four months.
Prior to the babies coming, she'll need to make sure she rests and enjoys lots of activities she normally does. If she enjoys cooking, she could prepare freezer meals, so she'll have some nice meals available for when she can't cook. If she likes to go to movies or other entertainment, she should do so, because it's harder to get away from the kids later. I spent months cross-stitching a stocking for my first baby, which I finished in the hospital the day he was born. I'm still working on the project I started once I came home from the hospital with him two years ago.
Baby 411 and Healthy Sleep Habits, Happy Child are excellent reference manuals, by the way. I hope this helps. You're a good friend to be helping your friend in this exciting time.