Bryce is actually a very good actress, but like nearly everything else in S3, it was a missed opportunity.
From what I understand , there was always going to be a girl who would serve to tempt Peter away from MJ , but that the producers suggested they use Gwen as sort of fan service and because of her play in Spiderman history. Of course that meant you had to introduce the father as well , but the whole thing was so bloated and done in such a half*** way, that it just seemed tacked on. I guess there were several scenes she had that were cut , but truthfully, I doubt they would have made the film much better.
It seems that , as far back as S2 , at least in the earlier concepts , that the writers tried to introduce a rival for Peter's affections since an early draft featured Felicia Hardy aka Black Cat. Then Raimi defunked S4 was going to try to bring Hardy back . Lol.