Is this odd for a fwb relationship? I [20/M] and her [21?/F]

So for some context. We've been acquaintances for awhile. She messaged me recently about being in an open relationship and basically extending a fwb relationship without her boyfriend being involved.

I've been in fwb situations but never with a poly relationship behind the girl.

Anyway, I've been getting off feelings about this being just a fwb relationship. First, she texts me constantly. Like, if I don't respond, I'll get 5 texts within an hour or two. I'm used to just contacting to meet up for sex/meet ups. She added me on Facebook. I generally keep my friends/fwb seperate. She specifically asked if it would be a one night stand or could we cuddle and other things too. She then asked recently if I would date her if she was single.

I clearly expressed being interested until I found an SO I wanted to date. Is it just me, or does she seem fairly clingy/not really typical fwb stuff?

I've never had to deal with an open relationship but from what I've gathered, I figured she was just looking for someone to have sex with on the side.

I'm not sure if I'm more used to nsa type fwb encounters, but she seems to be looking for companionship as well, which I figure she'd mainly want from her relationship.