She tries to give it back, I think the difference between her & Joe is that Joe's insults tend to get quite targeted and personal to the point where it's not funny, Dianne's tend to be a one liner in response to something said. Joe also makes some pretty mean comments about her in vlogs & she doesn't even be there.
Neither are faultless in the relationship & both disrespect the other, but for me the big difference is what Joe says has affected her, to the point where she comments that she's not smart enough or something along those lines. She ain't bright, but the fact she puts herself down ain't right.
Dianne also bigs up Joe's ego far more than she responds with insults. She is forever going on about how proud she is of him in vlogs & how amazing he is. Joe just has to scratch his arse and she posts about it like he found the cure to cancer. While Joe actually tries to put her down & belittle her when she teaches him how to dance, as though she doesn't have years of experience in the field.
As for the excercising, I don't think she forces him, I think it's more like I'm going do you want to come, & I think Joe is more afraid that she will meet a guy who is hot & not a complete ass like himself, that he makes himself go just to keep an eye on her. TBH he needs the excercise, he should probably work on his core strength for their tour, as he was barely able to lift her at the end of the Strictly special.