Have your mother get some rehabilitation training, and have your father watch to see how it is done. The rehabilitation instructors can also help show your father how to assist as well.

If Mom is in VA, check out https://www.vdbvi.org/ (if not, her state will have an equivalent.) Applying through the state will likely give her access to a wide variety of services including orientation and mobility (cane travel) classes, relearning how to use technology, how to manage in the home, etc. There are likely also organizations that work with blind people in her area.

One thing to look into (if she's open to it) is finding a therapist who is experienced working with disabled people. Losing your vision is a big deal to process emotionally, and a lot of people benefit from one on one therapy or group sessions with others who are blind/VI. Local blindness organizations are a potential referral source if they don't offer it in-house.

There are numerous options for continuing to do the things she loves. If large print books aren't suitable, there are talking books (check out the NLS, bookshare, nfb newsline) and desktop CCTV magnifier systems.

Some theatre programs (for example https://www.tdf.org/nyc/42/Vision-Loss ) now offer audio description for blind people.

If she's given the right tools and support, she can very likely maintain the independence she would have otherwise had at this stage in her life.

My great-aunt went through this about 3 and a half years ago, and while most of her vision is now gone, we have found some tricks to help her. For a long time she could use her peripheral sight to see things in detail, I don't know how it works but she stayed a pretty active knitter for a while doing that. We also got her a subscription to an e-book service and she adores it. Also Alexa and Google are really handy from what I've seen with her. She tried both but I can't remember which she liked better. Other than those things in my extremely limited experience, I know that listening and validating has worked well in a myriad of situations for me. I hope some of this helps, or at least gives you some ideas. I believe in you.

Look into contacting the Massachusetts Older Individuals who are Blind program, which is called "Social Rehabilitation" in MA ($1). It's designed to provide rehabilitation and other independent living services for people who become legally blind later in life and is free. Even if your mother is not legally blind at this point (or never progresses to legal blindness), they should be able to provide direction and resources. Please PM me if you'd like the program director's contact information.