Accident at pre school 💩

My daughter started Pre School this week. This is her first time away from me and surprisingly she has settled in so well - so much better than we thought! She’s been toilet trained day and night for well over a year with no accidents for months!!! I was so surprised when I picked up her one day from Pre School with the teacher telling me she had a little poo accident (not enough to get completely changed, but she did have to change her pants of course) so she must’ve stopped herself. She got quite upset the teacher told me because she hadn’t done an accident in so long! When I asked her why she did it, she told me she didn’t like the Nursery toilets and mummy wasn’t there to help. Tbh, I am always about to help her when she needs the toilet because she such a a tiny little 3 year old, she needs help getting on the toilet, even with her step. Is this normal? I know she’s in a completely new setting with different people around, but I just don’t know how to overcome this fear she has or how to help her feel more comfortable to use the toilets there. Since then, every time I go to pick her up, I’m waiting anxiously to see if she’s had a clean day! 🤦🏻‍♀️ I just want her to feel comfortable there and I don’t want this to put her off because she is doing so well there already!