TL;Dr. What's the line with hooking up with potentially emotionally vulnerable people?

So I've been forcing myself to be more outgoing and positive. I've gotten a lot of progress in confidence behavior but I think I've let it myself get carried up in the moment.

I had a night out with my roommates sisters, one my friend's SO, the other had for the second time have a SO commit suicide several months ago. We're all out having a good time and bar hopping. When the night ends she picks up her stuff from my buddies house and comes over to use the free room at my place to sleep, my roommate/her brother isn't home.

She sits on my couch, I offer her a drink and we're listening to music. It's 3am, she doesn't seem like she's itching to go to sleep. We talk and kid around, I sit down on the couch and I'm just in the moment, ask to make out.... We fool around for about 20 minutes. It's fun and light hearted, physically we click well. She's very into it and playful. She's totally cool and I've forgotten completely about her past issues.

Then she wants to go to sleep, I offer to be a cuddle buddy, she declines and alludes to "you wouldn't want to if you knew me" (she didn't think I knew her about the boyfriend and husband)

I tried to lighten things and was genuinely interested in just chilling in bed for companionship, no hanky panky but I could tell that was that.

So she's gone when I wake up and I just kind of feel bad for not thinking about the implications of possibly accidentally "toying" with someone who's been through a lot recently. I mean she's already dated at least one guy about 4 weeks after this bf died (the deceased were both abusive shitheads apparently)

So I really vibed physically with this girl, as superficial as it might be. I just think I'll be judged almost like taking advantage, since people like to assume the worst. I really forgot she had been through a lot, she didn't act like it and was quite cool i just felt her interest and we were both tipsy, but it still feels off or at the very least she's not a great judge of character so her being interested in me is not a great endorsement.

I'm probably crazy but as someone building confidence I recognize it's easy to be overly positive and "in the moment" and not be intentionally negligent with peoples emotions but accidentally being cavalier.