Rehab folks, by and large, know what they are doing. Whether she is pushing too hard or not hard enough-- they will tell her and they will appreciate you backing them up in how you offer her your support.
Where things tend to need a close look from family is in the basics of nursing care and mind-activating activities and socialization, because these are hard to give en masse and they are essential foundations to recovery and health.
The bigger facilities usually have a series of units, such as for immediate recovery and, later, for rehab-- since different levels of skilled nursing care are required at different stages, they group the people in units and "graduate" them from one unit to the next.
Rehab usually goes well, but it's important not to make promises about what outcomes she can look forward to. She may need to be extra patient with herself-- bones don't always behave the way we would like. The main thing is, all effort in rehab is rewarded, not always how we would like, but it's always better to rehab than not to rehab! :~)
Rehab is hard, hard work.... good idea to let your mom know you have confidence in her ability to sustain it and that it's OK not to be perfect-- such as, she may be too tired to fix her hair the way she usually does, etc., and worry she's letting herself go to hell. (She's not. She's doing hard physical work, that's all.)
You can also let her know, if she needs to know, that one of the most important factors in rehab to keep in mind is, it's to strengthen her to sustain the NEXT physical assault on her independence- Hardi's dad was poorly motivated on his stroke rehab and so when he broke a hip some 15 years later, by then he had lost so much muscle that he could not mobilize for the hip rehab... the consequence of not giving 200% to rehab is, sadly, less strength to meet the next crisis.
Encourage her to just let the professionals take her down the road back to as much independence as possible. Help her absorb the straight talk she is likely to get-- be careful not to dismiss it as her discouragement. She will need to work with them to the best of her ability.
On the other hand, you don't want her to push so hard in rehab that she prolongs her recovery instead of using it efficiently. Bone-knitting is hard work that needs lots of sleep and relaxed rest.