Need Insurance help!

Asking in regards to my mother (50F)… I don’t think she has ever had insurance since divorcing my dad 25+ years ago… and she’s really one to avoid doctors. A couple months ago her shoulder went out and she’s been living in excruciating pain for months at this point and lost all mobility in her arm. She can’t wash herself or do much of anything really. She swears it’s a rotator cuff injury but that hasn’t been confirmed. Two weeks ago she finally went to the ER and they took a CT scan. From what my step dad told me, they couldn’t find any major injuries to the area but told her that her shoulder is frozen and she needs physical therapy. I’m going to visit her and my step dad in a few days and I want to push them to look into getting health insurance because the only way for her shoulder to get better is ongoing physical therapy. The pain is also so bad that my mom insists on being homebound so they are looking for a physical therapist to come to their home. Sorry, that got a bit long. What I’m wondering is will an insurance company cover her with her injury already existing? Is there any way that an insurance company/policy can back date coverage to lower the cost of the ER visit & CT scan they already got? Any advice is appreciated