Is that the only way you see it? I took it to be deliberately confusing in that, it could either mean Bella/Jolina (The sister and friend that prefers woman - Jolina is bi so it's at least possible)
But as you say, it could also very well mean Debbie (The sister "Katie" and the friend that prefers women)
It's a very nice set up that it could be either parties/group to keep us guessing, that's why I liked that fortune teller scene so much, nothing concrete but inching towards answers. I will admit Debbie is the last person I thought would be in anyway involved ... guess I'm back to everyone on the shit-list.