Thanks everyone for the help. I'll see what I can do.
My daughter is just under 3 but her language skills are far above that. She's very particular - everything had a place and a purpose. She even voluntarily cleans up her toys (for the most part) before starting a new activity. OCD cannot be diagnosed until kids are much older - I just call it "toddler OCD." She just pays attention and is organized. Multiple pediatricians have assured me that she is "within the range of normal." :) It's just something to be observed for now. She's the "Teacher's helper" at preschool. She's a girly-girl, likes taking care of her baby dolls, and likes to "play teacher." Some of her dolls get put in time out for biting each other and not following other rules. :)
Anyway, thanks everyone. Most of the books MIL has written on are children's board books. Nothing special that deserves to be written on (Like a special copy of the "Night before Christmas" we had when we were kids, given to use by a special family friend who signed it.) And, yes, some plastic toys, and the tags of some clothes (ink ran once and marked up part of the shirt).
But yes, we will eventually donate these books and don't want my daughter's name on them! Good point! That's a safety issue! Thanks for the sticker idea, it may work in some of the books -- but at times MIL writes in all caps in blank ink diagonially across the whole inside front page! (or the back page, depending on the book).
It is completely aggravating to me. But lots of things about MIL are like that. Sigh, that's another saga...
Thanks, everyone!