Is it (serious) flirting?

I've worked at my current place of employment for only about four weeks, and I can already tell that this girl is definitely a flirty type. It doesn't help that she is the only girl in her area.

The other day, she was having a conversation with someone else about babies, I'm not sure how it started, but as I walked up to them the guy said "It won't be MY baby!", and then she points at me and says "It'll be his!"

I just kind of looked at her like... what? And she explains, "You and I are going to have a baby together, because that way it'll be tall and not short." I just took it in stride, but it was kind of weird lol.

Also, she will work directly behind me without me noticing, facing away from me, and when I step backwards a little we bump butts. If it happened once I'd say it probably wasn't intentional, but it happened twice in one day and never before that. And she gives me a huge smile every time we look at each other, though not sure if that's something she does for everyone or not.

Anyways, like I said, I think she is quite flirty, so it's hard to tell if she is 'just' flirting, or 'actually' flirting? And I'm not sure how I feel about it anyways, unfortunately even though she seems nice, she does smoke, and I am pretty cautious around flirty girls. They usually aren't good for stable relationships, which is what I'm looking for.
Is it (serious) flirting?
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