MIL not speaking to me- Idk why...

I'm sitting here in the dark about her feelings, and I don't know what to do or what to think. It's unsettling.

Here's the story: I'm 29 weeks pregnant, my husband worka out of town, my sister in law is incarcerated, and I, along with my mother in law whom they live with, have been taking care of sis in laws 3 kids (7, 5, and 1) for the last few months. My MIL and I have a great relationship. I love her to bits, and vise versa. But working together with the kids has put a bit of a strain on our relationship. Obviously things are a bit different now. We're having to co-parent children that are not our own amd are going through a seriously hard time without their mom (acting out, disrespecting, etc.) Anyway, I've noticed that MIL is a little less friendly towards me lately, and the past couple weeks have taken the cake. Some incidenta have happened under my supervision of the kids- the 5 year old cut the 1 year olds hair, the 5 year old had a screw driver and was playing with it that I was unaware of, and the 1 year old tripped over the dog and busted his nose on the tile kitchen floor while I had my back momentarily tured to him. My MIL blew up at me finally and told me that she didn't want me watching the kids any more. The next day, I wrote a lengthy apology and come to heart text and sent it to her. It's been 3 days and I've heard nothing back. My husband hasn't heard anything from her. I'm emotional and sitting with the feeling that she thinks I'm unfit and her feelings about me have changed. I just want to hear SOMETHING from her. It sucks. We had such a good relationship. And now it's all screwed. And I'm wondering if I really that careless or if accidents like that happen all the time? Ive watched kids all my life and nothing crazy like that has ever happened under my supervision. So I feel like I was just unaware of how much precaution I shouldve taken with them. But I honestly feel like these kinds of things happen under the supervision of the best parents out there. And I also feel like there's a lot more to my MILs silence than this. I just can't figure out what, and it's driving me crazy. Ahh! Idk, any thoughts? Similar experiences?