M.C.
I bet your mom will figure something out. Grandmas have a way of getting our little ones to do whatever needs to be done. She probably does not need much more than several 1/2 hour naps at this point esp. if sleeping well at night. There are enough things to stress about when you have a baby. This should not be one of them, unless a week or 2 go by and her sleep is totally messed up. If this is going to be a long term solution, your mom will figure out something that works for them during the day. It is wonderful that Grandma is caring for her while you are at work.
Oh, and by the way - my 2nd one slept through the night at 2 months, but when she began to turn over by herself, she'd wake herself up and cry. I realized after about a month of picking her up to make sure that she was OK that I had made a mistake. If I had let her cry a little bit, she would have gone back to sleep on her own. It took a really long time to reestablish her sleeping through the night again!! Let her fuss for a few minutes at night if she rolls herself over!!