Great point. I was thinking something really close-range. Also, maybe the serums she'd make wouldn't be too strong, so it'd take multiple doses to knock them out or something?
Hmm... Would you mind maybe picking another weapon, and that can be like her "last resort" type of thing? It's a cool idea, so I'd like to see you use it, it just concerns me. So if it's her last resort, maybe you could say she isn't sure how the serum will effect people, so she tries not to use it since she doesn't like hurting people.
Also, if you wanted to play the crew's "medic" or scientist or something along those lines, I think she'd be good for it. Up to you, though, just an idea. (She can still fight, of course.)