I don’t think being married/ long term relationship young means you miss out on anything.
I met my boyfriend at University, afterwards we moved in together and rented for two years. We are now planning to buy a house together (although not get married or have children so I guess in that way I differ a bit)
I absolutely do not feel like I’ve missed out on anything by choosing to have a long term relationship with my partner in my early 20s/move in together.
We both meet up with our friends (pre pandemic I went travelling with mine and I often go on girls holidays and out for drinks). Additionally, I still make sure I have time to myself, be it going shopping or just going out for a walk.
Actually, I’d say I have more spare money to do things I enjoy because all my living costs are halved with someone else. I also have the happiness of someone to live my every day life with/ go on days out with/ go travelling with in addition to my friends.
I actually think it’s more common than people think, I would say I have about ten close friends and out of those 7 are in relationships, the important thing is ensuring that your daughter still retains her own friends and feels the freedom to go out and do things on her own.
As others have mentioned, we have calculated that buying a house young will also give us financially security and being in a relationship hasn’t caused us to limit each other’s career in any way.
Finally (sorry for waffling I just really wanted to give the perspective of someone in a sort of similar situation) everyone is different. I genuinely don’t enjoy going to nightclubs or getting with random people so even if I was single I don’t think I would be spending my time doing this. I think it’s a bit of a romanticised view as I did a bit of it at uni and spent half the time crying 
Everyone is different, all that matters is that she’s genuinely happy x