Grammy wants to take baby swimming

My MIL wants to take my 10 month old baby girl swimming while she babysits and I don’t know if I want her to. What would you do? What would you say?

Edit: MIL doesn’t follow the best instructions. She’s forgetful and not a great swimmer herself. She only knows how to doggy paddle.

I’m a very strong swimmer myself and can’t wait to take my baby girl for the first time once it gets warmer out. So my MIL is asking to take her before us and with her not being a very competent swimmer, we don’t want her to. She takes everything we say very personally though so we’re looking for advice on what to say.