SSR 12-2p
Now is the time to file. She has already given up a potential of two years of payment by waiting three years. SSA can pay 12 months back from date of filing, but she needs to file now.
The process can be long with lots of time when nothing seems to be happening. If she is denied initially (30% approval on initial claims) and goes through the appeal process, it can easily take a year or more to just get to have a hearing in front of an ALJ.
If she waits until July, she will have lost one more potential month of payment. She can work on understanding the program while she is waiting for a decision, but it is time to file. Now.