Have dealt a lot with this in past years. What I tended to say was 'now put your arms in your sleeve, dear!'. That is, as little as possible- once I had dealt with everything I could deal with (e.g. investigated any problems at school). Some things you can sort out/exercise choice about, but there are other things that dc's (and adults) have no choice about.
In my dd's case, a lot of these things have been painful and upsetting. Getting up to go to school when you are frightened of physical pain is horrible, but believing that you have the choice to stay in bed is hardly helpful: you'd end up very ill.
Ds was frightened of speaking English when he started school (though perfectly competent). Again, not much choice- we do live in England. I'd have done him no favours by pretending there was a choice.
He was also frightened of his first male teacher who had a loud booming voice; if I had given in to that, he would have carried on believing that this teacher, and possibly male teachers in general, were scary. Instead, I forced him to go in and cope; by the end of the term he was absolutely in love with the man. He cried when he announced his retirement.
Dd was often frightened and cried at the start of reception- but had totally forgotten about it by the end of the day. If I had listened too closely, she would have missed hours of fun and all the friends she made.
And that, I think, is the cue. Your dd cries in the morning- does she carry on being unhappy all day? Ask the teacher! If she does not, then don't worry. It may not mean much. If she is genuinely unhappy throughout the day, refusing to join with the others and never seem to enjoy any activities, over a period of several weeks- then you will have to think again.