I suspect Finley isn't sincere about Paige, and if Rebeca has said she wanted to couple with him he'd have went like a shot.
And that's what's caused Paige's outburst, she feels he's not sincere, not really into her, just using her, and the "yeah it's alright" , not looking at her and not sitting beside her, just tipped her over the edge and confirmed it.
If you watch it's always her flirting with him, her playing with him, he seldom to never becomes affectionate with her.
As said, I think she suspects he's in it for the game and will be off it someone better turns up and it's royally pissed her off/hurt her feelings, hence why she got so angry.
So it looked to everyone like she over reacted, but in reality there was an under lying issue and that was just the straw that broke the camels back.