First off condolences on your dad passing!
I wouldn't use the term catastrophic, but if you leave it as is and it freezes it's going to cost a bit to get it fixed, chance are it will not and there it will sit.. They way I look at it is say you get it up and running and it fails with out her knowing about it, that could be an issue if freezing out, not to mention she might have to deal with it if your not around.. I think you made the right decision in draining it, least till spring, then you can come back get it up and running and have the time to teach her how to use it.. There are many here that would be willing to help with the questions..
Question is, does she want to use it and or do you think she will use it? If not one option would be to sell it, it appears to be an older spa with rusting control box and probably is failing frame/structure wise, may need a new cover yadda yadda. Older spas that tend to sit will start to deteriorate very quickly, might be better to get it sold while you can?? I don't mean to offend but I see this as many other spa people here probably do as well. Just some food for thought!
Also along with draining it, you should loosen the pump fitting and just leave them open till you refill it..