The letter confuses me because the husband refers to it as "our" bathroom, which leads me to believe it's a master bathroom, which leads me to believe there is a guest bathroom. If so, the painting can stay since the mother can make use of the guest facilities and will never need to enter the master bathroom to see to nude painting
If you're visiting my home - especially if you stay overnight - then I am fond of you and will make some changes to accommodate you.
When my closest friends come to visit for more than a few days, I purchase specialty grocery items for them. I have also stocked up on extra blankets and pillow for my best friend, "Wanda," who gets cold easily and likes to sleep with 6-8 pillows.
I will not purchase specialty cooking items (e.g. coffee pots, pans) unless it's something I will be able to use. My kitchen space is limited; I am only "spending" it on items that I can use for me.
Would I purchase a specialty brand of Vodka (or orange juice or other liquid)? It depends. How much does it cost and, why do you need it? I'm not running a high end resort; you’ll get basic beverage choices. I have water, juice and wine. I don't see the need to provide much beyond that.
I really can't see taking pictures down from the wall. "Redecorating" is a much different request from having a specific food item. It's not one I would really honor unless I had good reason.
I would be interested to know why she felt /now/ that it was unacceptable to. I don't fault her for wanting to leave it up, but I can see where her husband is coming from- I would feel comfortable displaying artwork with nudity in my home, but probably not around my parents, and it seems like his mother is already very wound-up about nudity in general. I don't think either party is in the wrong here, but they need to chat out the underlying reasons for the picture staying up or coming down and what it means for them.
Maybe it's a pain to remount the photo on the hooks? I have my parent's wedding photos in my upstairs hallway. The particular hooks that I used make it somewhat difficult to rehang the pictures (I've had to take them down multiple times due to an issue with flooding and having my home soundproofed). This is not something I noticed until after I had taken the photos down the first time.