I don't think she's ever truly gone over the top. My opinion only. In comparison to all the others in the show, she kept it normal and realistic till the very end. At least I would not describe it as over the top. But I see and understand what you mean and refer to. I would just use a different word in my own commentary. I would say that at some point it seemed like she didn't care as much. The scripts were so, so bad... she was made to yell at Brooke - you whore, you slut, you prostitute every single month... so at one point it felt like the venom was turning into repetitiveness and just... boredom. Just the fact that Brooke started laughing at her insults in the last seasons... is telling. Stephanie stopped having her threatening and powerful presence - she became nothing more than a guard dog for Ridge and his children. They also made her more brutal and inhuman like (arranging a strange man to come in Brooke's house, giving him a key, which is basically accomplice to RAPE). They did give her some of her own storylines... her father's abuse... her mother passing, her cancer... even Pam... but still... the biggest portion of the material was her telling Brooke how she is a ho. It could have worked if it was done more sporadically.
And ever since they made Stephanie to be some kind of... lying ex-slut herself with the 2001 rewrite of Massimo being Ridge's father (incredibly wrong rewrite if you ask me... and made only to serve Brooke and give Ridge a new brother who Brooke can sleep with again)... the whole... high and mighty Matrona-persona just... flopped. Brooke started telling her that she doesn't have a moral high ground anymore and in a way she didn't. And Stephanie yelling at Brooke how disgusting she is... was not hitting the same way. STILL, these two women gave the show a sense of purpose, of continuity, of familiarity even. We loved to see Brooke and Stephanie at it. Of course nothing compares to the original war circa 1987 to 1993. Nothing. There were glimpses of powerful moments (2005 was a great one with Stephanie's heart attack)... but... nothing was ever the same. We all know why. Bradley Bell turned the show into a badly written Jerry Springer episode.
So I would just say that... there were moments where Susan was not giving her usual 100 percent and I felt it. Even when uttering an insult, it was not the expression of real hate that we used to see. The energy was not there all the time. But she was STILL turning it on regularly when she had to and I will repeat myself - tranformed sh-t to gold many many times. The show really breathed its last breath with her death.
Just this last scene... is a testament to that. Susan... giving a quiet, yet powerful performance in her last minutes of a 25 year old role.