The thing about labels is that they also contain instructions. My own DD is on the spectrum and I know how difficult it can be. Especially when they seem "normal"
These early years are hard but without a diagnoses, the teen years can be unbearable.
I'm not saying your DD is on the spectrum...it might just be immaturity ...she is only six after all but diagnoses are very useful because they allow kids more leeway in school.
My DD also has difficulty with transitions....she's not treated any differently at school but her teachers understand her better thanks to the report we got from the educational pyschologist. That means they don't punish her for behaviour she can't help such as being late.
For now, try these strategies with transitions. When she's in a calm, happy mood ask her if she'd like to help you make yourself a calendar of activities....for you...not for her.
Do it on a sheet of cardboard and have stickers to decorate. You can include things like "Wake up, get dressed, clean teeth," and so on.
Separate each activity so it's clear to read. Also include "Play on phone" or "Read book" or whatever your hobbies are. Do separate days. Add times for each activity.
Then ask if she'd like one for her too. Refer to your chart and hers...as each day unfolds.
"Oh look, it's time for my book!...yours says that when you've finished your snack, you should be having a bath"
She can refer to it herself for a reminer of what's coming. A lot of the difficulty is around control. She can also alter the order of things if she asks...make sure this is an open thing that she knows about.