I think THEY want to wrestle her. Most the time Ab is either just on attack, or defending herself from their poking, groping, tickling, and pinching. Her "happiness " looks like anxiety and stress reactions.
Don't forget, Asshat's Mom started the whole family wrestling stuff. She used to do it with Assa and then she started doing it with him and Isaiah. I think there were a couple of vlogs where she sort of did it with Abbie but obviously on a much milder level.
I know that we generally have a very positive opinion of Asshat's mother but she does have her faults, too. This family wrestling thing is kinda.... odd.
Most definitely Abbie is reacting a lot of the time to their behaviors towards her. They tickle her and mess with her whenever they feel like it. But if she tries to initiate it -- in the same way that they do to her -- that's deemed inappropriate and she's told off for it. Now she's being told to ask first. Which, let me be clear, the concept of asking first rather than just going for a grab, a tackle or a pinch IS important. But I think Abbie ought to be afforded the same courtesy.
I also agree with what others have said that I think it's a horrible idea to encourage her to be physically aggressive. Regardless if she asks first or if it's a sensory fulfilment. She has other behaviors that would fall under the sensory fulfillment category but they are unhealthy and harmful -- they don't let her continue with those ones, right? Or they at least try not to. The wrestling should be no different.
Asshat sees nothing wrong with it because that's how it was with his mother. He was raised to think that's just normal family bonding. He just adds in the "Abbie needs deep pressure sensory input" to put a bow on it and make it look nicer. Well, he tries to.