My mother in law wants to babysit alone, but I'm not comfortable with it

(TL;DR at the bottom, this became a bit of a novel, sorry)Hi all,A little background:I have a 21 month old daughter, happy, healthy and active. Until recently, my in-laws babysat her one day every week. It was always either both of them together, or just my father in law (FIL), because my mother in law (MIL) has had lifelong issues with her hips and two recent hip replacements, so she has some limitations in terms of mobility (walking, lifting, standing for extended periods of time, etc.).A while ago, my husband and I felt like babysitting for a whole day a week (and travelling to and from our house during rush hour etc) was getting to be too much for them. After several times of them denying this (I think they were afraid of losing that time with DD), recently they admitted that it was too much, so we cut back. We now have daycare four days a week (I'm home on Fridays), and if they want to come and babysit for an afternoon every now and then, every week, every other week, whatever, they can. But there's no obligation anymore.OK, so far, so good. But. The last time they came to babysit (which was still a whole day, we didn't have the extra daycare day yet), my MIL came in the morning, and my FIL would be there a couple of hours later. I wasn't super comfortable with leaving DD alone with MIL because I'm not sure she's physically up to it, but since they only told us at 10PM the night before, we didn't really have much choice.So I came home after work, expecting both my ILs. And only MIL was there. Turns out FIL didn't feel well enough to come babysit after all (he had his reasons, but still). I was a little taken aback, so I didn't make a big deal (even though I really didn't like it, especially the sneakiness of not mentioning this at all), but I did mention something like 'I thought you weren't comfortable looking after her on your own MIL so I'm surprised FIL isn't here'. And my MIL had this whole list of reasons ready why it was fine and how she'd managed everything.To be honest, this didn't put me at ease at all. Hearing how she'd managed to get DD in and out of bed, onto the changing table, into her high chair etc by rather elaborate constructions only strengthened me in thinking it was physically too much for her. And more than this; what if they're out and about and DD dashes off the sidewalk? Will she be able to stop her in time? Or what if DD squirms a lot when being put in the high chair (a regular occurence); will she be able to handle that? MIL claims it's no problem, but I see that differently.Now, on to the issue at hand. In laws are super happy with the new daycare arrangement. And they've decided they want to come for an afternoon every week. BUT. They want to alternate. So FIL one week, MIL the next.And there's the problem: I am not okay with that. So I talked to my husband, and while he believes his mom when she says she can handle everything, he also feels that if I'm not comfortable with this, we shouldn't do it. So he called his mom and said look can you guys both come this week (instead of just MIL), so we can talk some things over. MIL immediately knew what it was about, and kept asking him why until he was forced to admit we weren't comfortable with her watching DD alone. And she was furious, apparantly. DH felt really bad, both because it just sucks to make your mom mad and hurt, and because he feels stuck in between me and her.So now this Tuesday my ILs are coming over, and we have a rather difficult conversation ahead of us. So I am looking for advice. How do I tell her gently but firmly? I am not willing to budge on this. I'm not saying it's forever; her condition has been improving, and as it does and DD gets more and more independent, I can see it happening in the future without this much anxiety from me. But right now I would just be anxious the whole time because I am 1) not sure she can handle it and 2) not sure she would call us if anything happens.Honestly, other than this she is a wonderful grandma and a nice MIL; I don't want to take away all babysitting from my ILs, as both them and DD enjoy it. I would also love to keep our relationship as pleasant as it is, so I'm not ready to take drastic measures or 'punish them' or anything like that. I'm fine with them babysitting her together (mostly fine anyway, still some hesitations there, but I'm more than willing to admit part of that is probably just my anxiety and a different parenting and communication style than I'm used to.)Wow, this turned into a much longer post than I'd planned. I guess I needed to get that off my chest. Thank you for reading, I'm very interested to hear how others handle situations like this.TL;DR: I don't think my MIL is physically up to the task of caring for DD alone, but she disagrees. Now I'm forced to explicitly state I don't trust her judgement in this and don't want her doing it. She is mad and we have a conversation about this coming up on Tuesday. Advice on how to handle this is much appreciated! via /r/Parenting https://ift.tt/2Rot0UG