Should I encourage my daughter to mask at school?

Hi,

Okay, so really I know the answer to this question, but it is much more complex than that. My daughter (9) hasn't settled into school since going back in September, largely because she has taken a dislike to her new teacher. However, last week we had the first 2 days where she was really great in school. Friday, and this week, we are just back to her usual behaviours of being rude and running out of the classroom. When I asked her what the difference was between those two days and this week, she said that she was just holding everything in [on those 2 days] and she can't do that all the time. 

I totally understand that 'holding it all in' all the time when she is feeling overwhelmed is not the right answer, but neither is letting it all out all the time either. She does need to learn some level of self control, and understand that not everything can be adjusted for her (she already has a significant amount of reasonable adjustments made for her). 

School, on the whole, have been very helpful (she did have FT TA support, which has now been reduced to PT as she still doesn't have funding yet - though this is due to the school messing up with the EHCP). When I asked them their advice, they said to encourage her to speak to a trusted adult when she is feeling upset, but the problem is she is upset and overwhelmed ALL OF THE TIME! There are only 2 trusted adults in school that she would speak to and they are not available to her all of the time. 

I honestly don't know what to suggest for her to do. I know asking her to hold it in isn't right, but she does need to learn how to regulate - but I don't know how to reach her to do this!