Hey there! Of course it is hard for allistic people to understand this since unfortunately you are full of stereotypes, whether you want it or not. So here are some news: all autistic people are very different! Also you don’t have to adopt the headcanon, of course - I just wanted other people to know its a possibility.

So again, writing just from my memory:
1. She is obsessed with magic to the point of it being unacceptable in a society of wizards and witches. This is typical for having a special interest.
2. She has social interaction issues. She doesn’t understand social protocol very well and has trouble making friends. She can’t help but infodump all the time, correct other people’s mistakes and try to teach them. She doesn’t understand why it can be annoying. She also has issues with distinguishing social layers and adjusting her speech (for when she is talking with her peers or teachers). She doesn’t pick up on malicious intent or some speech tones (for one she doesn’t understand that Snape won’t give her points not because she isn’t smart enough but because he is personally against her).
3. She is obsessed with rules, plans and schedules. When people break rules she freaks out not because it is morally wrong, but because it disturbs her routine. She has no problems breaking rules during Umbirdge’s run because she understands that it is justified so I make a conclusion that she sees comfort and stability in following rules.
4. There are descriptions of her stimming in the book, even flapping her hands. I don’t have spoons to look for quotes so if someone can find them, please do.
5. She has tangled and bushy hair because taking care of it it sensory unpleasant.
6. There are some descriptions of her having a meltdown in the books.
7. She has increased compassionate and affective empathy with low cognitive empathy. She is very affected by other people’s emotions but she can’t interpret them very well. One good example of it is the house elves story - she wants to help them even though they didn’t ask for it because she can’t decipher that level of emotions.

These are all autistic traits. Considering that no where in canon it says that she is allistic, logically I make an assumption that she is autistic. It is more probable. Hope this helps!