First of all, unless you actually asked this person for feedback, it was INCREDIBLY rude of her to come along with a list of criticisms. Especially as she was not even the party host, so it was none of her business. Her behaviour was much more socially inappropriate than anything that you may have done or not done. Did she say these things in front of your child? If she did, that makes it even worse!
As regards the specifics:
(1) The gift is the one thing where you may have slightly erred. It's usual to bring a small gift to a child's party, though especially right now it should be recognized that not everyone may be able to afford to. But it is much ruder for her to keep tallies on which other guests brought gifts than for you not to bring one.
(2) Not making small talk with other parents is not a big deal. The only thing I can think of, is that maybe someone tried to get your attention for a conversation, and you didn't notice because of your sensory issues. I'm not autistic but I have some visual processing problems which can occasionally make me unaware of people approaching me from a distance, and sometimes they might think I'm ignoring them. But even if this happened, they should face you and speak directly to you (after all, many people are a bit hard of hearing, and would need this).
(3) Unless you actually got in people's way, which is not what she's saying, there is nothing wrong with a bit of 'hovering' where children of this age are concerned. At 7 or 8 maybe; but not at 4 or 5, even if your child had no special needs. It sounds, from (2) and (3), as though she saw the party as mainly a mothers' get-together with the children as an excuse/ opportunity for that, while you saw it as just a children's party with the mothers there to supervise. I am sure that there were others with the same approach as you.
(4) Again, unless you were actually disrupting something, or getting into private areas of the house, there is nothing wrong with leaving the room occasionally.
(5) Did she say what she thought was inappropriate about your clothes? It doesn't sound as there was anything wrong with your choice of clothes. What was she wearing?
At any rate, she sounds horribly rude!