How broken is Gwen on the inside?
Why the the hell did she fall for the creepy kid who has mastabatory aids of her on his computer?
The stalker who follows her to work?
The rapists that tries to break into her bedroom window?
Or the sociopath who runs through the streets at night thrashing people to within an inch of their lives?
Not even daddy issues would explain this choice in a perfect mate who just might be minutes away into metamorphosing into a 20 foot tall carnivorous spider... Although?
If Peter did turn into a spider, at the climax of sex with Gwen, he would demand and insist that she eat him, so that he could get off too?
So I suppose it's less dangerous for her, if Peter turns into a spider than if he stays a man.