Raina is fascinated by Peter. Not only is he potentially from the same universe as her (she believes they are, but she knows there's no telling for certain), but he also knows and interacts with the Kree, he saved the whole universe from some crazy Kree guy, annnd there's something about him that, while he's still a hero, he's not as wholesome as say Captain America.

Obviously this guy has a lot of good stories to tell, and Raina intends on maneuvering herself into a position where he might be more open to telling her them. Plus he's some nice eye candy! So she certainly doesn't mind flirting and being all over him.

I do think that of the people Raina knows, Peter probably has the most potential for her to develop a friendly affection toward. Peter's spent his whole life around criminals, so he's probably not gonna be too judgmental of Raina's level of shadiness. And the fact that he wasn't openly repulsed by her when she showed him her thorns goes a long way. (Raina's so insecure about her alien side, man! And Peter sees that weird shit all the time, so he probably wouldn't even flinch at her true form!)