Some of the above sounds sensible
but please beware OP that a lot of the advice in this thread may well be from parents with no experience (yet) of parenting this age group 😅
so easy to imagine how you would just not stand for things even in reality things creep in and young people do things very differently from how we did things at their age. It is a different world now.
also this age group has had a massive setback in their social development from COVID restrictions and anxiety and social anxiety are very commonplace
my DS at 19 started going out with a girl a bit like this, She was shy, and anxious, and to start with e we wanted her to be comfortable so gave her lots of space
So I can see and have experienced how this sort of behaviour and set up creeps in
i have continued to ask her to join us for dinner and occasionally she does
i have not set it out as a rules thing but more as in we would like to get to know this lovely girl of yours a bit better 😁
also took her out with us for a meal of few times, so over time things have changed a bit but it did require some effort
i am not big on the laying down the rules approach but everyone should parent their young adult kids how they see fit.
just a perspective from someone who has been in a similar situation 🙂
bit of coaxing like “come and have some pizza with us tonight, we would love to spend a bit of time with you 😁”