The thing is, that's not putting your DD in the best frame of mind for learning either - it's counter-productive to be getting that upset every day.
It's also not as if it's the second day of school - we're nearly in December so presumably this has been going on since the start of September and not getting better?!
I have just been thinking about this some more and I think I would now be at the point where I'd be talking to the teachers. Getting that upset every morning is just awful for your DD and actually, pretty awful for you too.
I'm guessing that as it would be a change in school policy you need, a chat with your class teacher wouldn't achieve much. Do you have a pastoral team at the school? We used to have a team that parents could make an appointment with if they were concerned about the child's well-being, which this absolutely is.
I'm just going to ask the question, no other signs of SEN? No difficulties in the classroom? No difficulties speaking up? Or unusually anxious at other times? Girls mask SEN extremely well - it often takes years to spot compared to boys.
How many children in your DD's class get upset like this at the gate - are there many? If your DD is one of very few, it would be easier for them to come up with a reason to make an exception. If there are lots of them, it would make more sense to change the rules....
If you don't have a pastoral team, you could ask for a meeting with the Head or Deputy Head. Or you could write a letter to the school governors.
People talk about "reslience" which is all well and good if your child only has to persist for a bit. When if you're talking about three months of crying every morning and anxiety to the point of not wanting to go in, that's not "building resilience" - that's a child communicating genuine distress who clearly isn't yet ready, for whatever reason. It's not a parenting fail either. We seem to have forgotten that children aren't tiny robots and they don't all develop at the same rate!
Also, I was a school governor for five years+, including acting head of governors for over a year. At our school we'd absolutely have been concerned about a young child experiencing this level of distress and we'd be wanting to help her succeed by creating smaller steps for her to achieve the goal.
You're absolutely right to raise concerns.