If she has not asked to be alone, don't assume she wants to be alone. Just ask her. When my son was very sick and we were dealing with a lot of horrible outcomes, we were very, very lonely since we have no family around here.
A friend of ours just hung out with us. We did playdates, lunch once in awhile and things like that in between what we had to do. It made a world of a difference just to have that to look forward to besides all the medical stuff we were dealing with.
Before that I was really struggling because any time we weren't doing medical stuff, we were planning more appts., planning more hospitalizations, talking about outcomes or dealing with insurance and it felt like that's all we had left in life. It was pretty scary. If you ask, you can get a feel for what she is really needing.
Other things that people did for us that may be helpful: make a dinner, even a frozen one takes the pressure off a day she needs to make dinner and helps her eat; offer to clean (after everything else, I did not have enough energy left in a day to do anything beyond basic straightening up for a bit), do some laundry, run some errands; offer to watch the baby for a morning so she can get some sleep; etc. I had a really hard time asking people to help, but if you offer to do something specific, it is a lot easier to take someone up on an individual offer.
Obviously with a new baby she already had a lot on her plate. Staying away without a phone call or at least card though can have the opposite effect when someone is dealing with something so big and scary and overwhelming. Just letting her vent and express her feelings could be helpful. She will be in our prayers!