I scanned though all the excellent advice and my advice would be the same as the majority, clean, press and grade the book for safe keeping.
The one thing I might add that I didn’t see is if the book is graded and you choose to not sell in the event your book is passed on to your heirs they would likely appreciate the significance of the book easily.
your mom was going to throw it way. If it was in a CGC case I bet the thought never crosses her mind.
I’ve lost both my parents it’s tough, my condolences.