It probably is some sort of means to an end. She hates Ollie cause he's a supposed killer, but yet, is teaming up with a known killer? Lol.

opportunism.
or she's blinded by revenge for her parents.
the creators said she decided to turn on oliver after he lied about being the hood and revealed the list.
while we watched ads, she was deciding to betray ollie.
maybe she views prometheus as a means to an end, like isabel rochev and slade