Eek! Guppies harassing new Platy

[ExtraHannah]

Well I picked up 4 Platy and 3 cory today to finish out my 27 g tank. Everything seems to be going fine except that all three of my little guppies are picking on the smallest platy - a Mickey Mouse. I think it's a female. I should have researched male/female better and been sure of what I was getting, but I think I have one male and three females. However, I didn't think the guppies would bother platy. They are just harassing her to no end. Thoughts?

 

[ExtraHannah]

Maybe I panicked too quickly. I've been known to do that. It was just so weird how they all three went right after her and kept at it for an hour or so. However, they seem to be backing down now and the platy is sticking with the other platy more. I'll still keep a close eye. I guess maybe there's going to be some posturing with new tank mates...