It's not over cautious and we have a similar situation. Dd1 (10) has been befriended by a 16 year old who lives near pil. They've had a casual acquaintance for a few years as mentally the young woman appeared much closer in age to dd1 than her own age. But recently the actual age difference has got more noticeable and with the passing of another neighbour, the woman has been knocking at my pil a lot more for my own dd1.
At one point I contacted the school the woman was attending (special school) because the constant knocking was beginning to upset pil as she wouldn't take no for an answer. Sadly the parents either didn't care or didn't understand that the daily/twice/thrice daily visits were not acceptable - she would knock not long shyer breakfast, again around lunch and even in the evening at times to ask for dd1.
It stopped for a while but recently it has started up again as the woman has found out dd1 has a phone. Despite being told she won't be given dd1's number, she persists in asking.
In your shoes, I would see about blocking her on roblox if that's possible (mine don't play). Your dd doesn't have to know that's what you've done.
When she knocks for your dd, it's ok to say now isn't a good time, you're busy, have plans. You don't know what time you will be done. Today isn't convenient.
At 17 it could well be that Sen or not, her parents believe she is out and about with her own peers and expect that she might be stopping with them.
Personally I would also speak with the safeguarding lead at your dc's school. Not because I think there is necessarily any issue which might cause harm. But because they will be best positioned to offer you and the young woman advice on the expectation of appropriate behaviour.