My girlfriend likes this girl she works with, and the co-worker likes her back. They’ve talked about dating, but my girlfriend doesn’t think she could handle dating someone who has a child. But I think it’s possible to date someone without becoming a parent to their child (I’m not sure if the co-worker expects her to be a parent or not). They still flirt, and I love seeing how cute they are. I think they’d make each other really happy, and to be honest, it’s hard enough finding someone who is okay with polyamory.
It’s pretty hard to date someone with kids without ending up as some kind of co-parent. Kids can be pretty sensitive to the relationship energies passing through their world, and it’s on the adults to be responsible about that. If your girlfriend is around the kids often, and clearly affectionate to their mom, if she is sleeping over, etc. the kids will expect her to be involved in their lives.
The partner and the parent can try to set clear boundaries: “Elgreth is Mommy’s friend, and she comes over to hang out with Mommy, but she cannot come to your piano recital/does not want to play Barbies/etc.” - but children are a ton of work, and will demand your attention regardless. If you’re dating someone with kids, you need to be present to those kids on some level.
Also, dating someone who is a parent means accepting that the kids take priority and being a grownup about that. Date night might get canceled because the kid just barfed up goldfish crackers all over the couch, so now instead of leaving him with the babysitter to have a nice adult night, you’re getting climbed all over by a potentially-contagious-but-still-rambunctious little one while watching the Minions movie on the floor because the couch is still damp. If you can’t handle how chaotic and demanding kids are - if you’re going to sulk about missing out on the night you have planned - don’t date someone with kids. If your girlfriend has the patience and flexibility to do that, great. But if not, she can’t just opt-out of the whole kids thing.
Your girlfriend needs to figure out, realistically, what she means by “not willing to co-parent” and whether that is possible when dating someone with kids. Not wanting to take them to doctor appointments or make 3am Walgreens trips for cold medicine is pretty standard for new partners - but wanting to sort of “date around” the kids or being unwilling to include or involve or make concessions for them is unrealistic and impossible.
Your girlfriend should talk to this person who’s interested in her and figure out what the other person’s expectations are as well. Some people with kids see themselves as a package deal and don’t want to bother dating someone who’s iffy on the kids thing. Other people might be fine with a low-key fling where they see each other when the parent is free. In this, as in all things, clear expectations and communication are key.