I think she will surprise you too and there will be significant recovery. Count on at least six months where she will indoubtedly need a lot of outside help. 1-2 months is a bit optimistic. It is unlikely she will have another stroke. She needs to go to a professional rehabilitation facility, if at all possible. The programs at such facilities vary, but she should expect to be there four to twelve weeks. Insurance and financial coverage are the deciding issues. I am very hesitant to blame hospitals, and probably there was no negligence, however the threat of a tort with a medical facility can often bring about a small concession, such as paying for above-the average periods of rehabilitation and therapy. As much as I despise bottom-feeders, it would probably be worth the time to obtain all of her hospital records and nursing notes with a subpoena duces tecum and pay for a consultation. Don't give up hope.
I am sorry to hear about your sister-in-law. This is a terrible situation but, unfortunately, not that uncommon. One thing that's going in her favor is her age. She will likely recover better than someone else in the same situation who is much much older.
Having said that, it is unclear how long it will be until she's able to live independently. The most recovery usually occurs in the first 3 months post-stroke, then some recovery still takes place afterward but the bulk of it would have already taken place. By that time, you will have a pretty good idea whether she is capable of taking care of herself and/or the baby. She will need extensive physical, occupational, cognitive and speech therapy while in rehabilitation. Also, in a month or so, she should undergo neuropsychological assessment to see how much cognitive trouble she has. She may very well be somewhat impaired but it may not interfere with her daily life and/or taking care of the baby. A good occupational therapist shoudl be able to assess how well she can manage on her own: cooking, dressing, washing herself and the baby, signing checks, shopping, etc. etc.
Make some arrangements for the next 1-2 months and then see how much progress she makes. She may surprise you.
Good luck!