That is not independance, that is teaching personal space

I would suggest the best way to teach social skills would be to expose her to as many social events test you can

Maybe attend social occasions outside of school. Eg a sport activity, organise play dates etc

Sounds more like your daughter also has anxiety fear of being alone. This is harder for her to understand as she may not know what that is. Her friend and you are her security blanket. With one of my children I did find it hard to get him to leave me alone for a few minutes, I had to do it in small increments by distracting him. This was hard for me to do but now he can leave me alone for 30 mins at a time and his two friends at school can have a break. Another son I have is the opposite can not get any attention from him.

How old is your child ? You tell the teacher say she has only one friend. What does your daughter say ? Does she like more children ? Or does she share interest with children of her class ? I would organize one on one playdates with classmates she feels some kind of connection with and observe what she’s doing. You might be able to help by choosing activities for her to do with her play date and or structuring it. You’re also very very important role model to your child and could play out a social scene together. In some area’s they have support groups for children with autism. See if you can join and find support from them.