AITAH for refusing to change my mother-in-law's diapers?

Wife's (55F) parents didn't do retirement/end of life planning well, and her mom's (85F) starting to need a lot more physical care. My (60M) wife is understandably stressing about it, feeling it all lands on her to solve. She needs help with her mom, which I gladly provide. But when we started discussing the potential of having her mom move in with us, she asked me to help with things like changing her mom's diapers. I said no to doing diaper duty. I'll help with a lot of stuff, but that's not something I'm willing to do. She hasn't spoken to me since then, the literal silent treatment.

For context, her dad went through hospice a few years ago, and I did help with cleaning up after him, including changing his diapers. That remains an unpleasant memory, and I can't repeat it with her mom. I've been clear I'll continue helping with other stuff - helping her move, get up and down in her chair, being her Uber for trips with her wheelchair, house maintenance, and so on, but i have to draw the line at diaper duty. She has a daytime caregiver who deals with all this stuff right now, but if she were to move in with us, my wife and I would be on the hook for night and weekend care.

Am I being unreasonable, or is her ask beyond the pale?

UPDATE: Thank you all for your thoughts on this. Seems to have struck a chord with a lot of people. Sounds like the majority of people here agree that it's OK for me to set this as a boundary.

Clarifications to a few things commented below:

• We've been trying to get MIL into an assisted living arrangement, but Medicaid doesn't think she's yet to the point of needing that, so they haven't approved funds for full-time care. But she is rapidly nearing that time - in fact, we had to have the fire department come and lift her off the floor today, she fell again. (She wasn't injured.)
• My wife decided to talk after most of the day not speaking with me, and her anger was less at my refusal than at the cumulative frustrations. I just happened to be the closest and easiest to take it out on. She still doesn't quite understand why I am very reluctant to change her mom's diapers, but I've let her know this isn't a boundary I'm willing to easily cross.
• MIL is mostly cogent, although she's definitely less sharp than she was. We haven't specifically asked her about changing arrangements and if she'd be comfortable with me doing that, so I don't know how she'd feel. Totally agree with commenters that suggest her comfort is a primary requirement.
• Also, to clarify, it's less about the yuckiness of the physical part (nasty as it can be), but more about my sense of propriety. And of setting what I consider a reasonable boundary, and expecting to have it respected.
• For the (thankfully) few people who stated or implied that I should allow others to set my boundaries... do you notice that people cover their drinks when you walk by? Just curious.
• Also, to be explicitly clear - I'm not refusing to help; I'm as involved as I think I can be. I'm just not comfortable with one requested activity.