need some opinions/advice

my mother in law asked me last night if she could take ella on her own this tuesday. i do not trust her to look after ella on her own and told her that it was easier for me if we saw her together in the afternoon when i am free. i know MIL is bugged about this and i have a feeling it will soon turn into a bit of a drama.
the reason i dont feel trusting of MIL to watch ella by herself is that she has been suffering from menopause and depression and a major symptom she has is chronic absent-mindedness. i know it sounds horrible, dont get me wrong i do love my MIL, but i just don't feel safe leaving ella in her care alone.
their house is not childproof so ella needs to be watched all the time when we are there. there is a steep flight of stairs with bannisters she can fall through, 2 unsafe balconies and an unfenced diving-depth pool.
twice recently MIL has forgotten that she'd volunteered to watch ella and one of those times i found ella on the stairs alone.
she's repeatedly left ella alone in the dining room in her high chair without straps on (because she can't work them) and gone off somewhere.
when we're out together MIL wants to walk with ella. i'm fine with that but ask her to follow our rule, that ella must hold our hand when we're in the street or she goes back in the pushchair. twice recently MIL has let her go saying "let her have a bit of freedom to explore" and not noticed when ella has run into the street. it scares the heck out of me!
i won't let MIL babysit unless i know that FIL will be there too, but i do try and give them lots of opportunities to do this.
i know MIL loves ella to bits, and none of these things she does are intentional but i just feel so strongly that i can't leave ella with her safely. she forgets SO MUCH.
sorry for the giant ramble, i just need some outside opinions/advice about this. am i over-reacting? and can i explain my feelings without upsetting her?
thanks x

No further advice, but I agree with Liz about getting your partner to have a quiet word with your FIL. You are not overreacting - if you were, you would have stopped all contact between Ella and your MIL regardless of who else was there!

OMG your post sounds exactly like my MIL.. she's not forgetful (that I know of) but does have other issues which mean I can't trust her to look after my Ella.. I have been avoiding the topic of her wanting to babysit Ella alone but I'm not going to let her do it until Ella is MUCH older.. I would be so worried the whole time if she did. I won't be letting her look after Ella until Ella is old enough to communicate clearly and to look after herself too. It is not selfish, it is to protect our children, I know I would be blaming myself if something happened, and I don't want to take that kind of risk.

Oh, just thought of something, I don't understand why they are so set on looking after the kids alone either.. it's not like it's their right, I mean, it's fine if you are comfortable with it but if not, they will just have let go of it.

I know exactly how you feel. My MIL keeps saying she doesnt mind looking after Hannah if I need to go do stuff or when I've got netball etc, but I really dont trust her to look after Hannah at the moment. Some of you know, but MIL had a brain haemorrhage a few days before Hannah was born and although she is almost back to normal physically, shes not quite as sharp as she was. I've so far managed to fob her off a bit, hopefully it doesnt become a prob.

Someone prob needs to talk to her, but remeber that you are doing what you need to to look after your little one and you are definitely not the only one going through this. Good luck