I saw in the position your stepdaughter is in, kind of, for 7 or 9 years. I don't even know how many years it was. I stopped going to a low level education, and didn't want to work.

Now I maybe went 'out' maybe 16 times in 9 years and didn't spend a lot of money on luxurities. But I sure cost my parents, and myself, a lot of money. As well as overall stress and regret.

But I cannot say what should have gone differently for me to get out of where I was.

I always thought I was lazy and stupid and avoiding all responsibilities, but there was nothing else inside of me. It didn't help that I felt zero appriation or encouragement from others (mainly because I felt none, though what was there was marginal as well) and had zero incentive for beign rich, succesful, getting status.

I am inclined to project myself on this case, and say it is not simple laziness with anxiety as an excuse. But unlike me, she is having fun with friends. I avoided both the hard work and the fun activities.

The usual argument is tht pampering is bad and the safety wheels should be removed. She should be allowed to fall and fail so she learns this attitude won't get her through life. If I project that on myself, I don't see how it would have 'helped' me. All my parents could offer me was financial support and patience.

Hopefully in your stepdaughter's case she has at least one parent that is able to talk to her about her difficulties. My father used to yell at me "You don't work, you don't go to school. I am mad!" and that obviously didn't help. He should have tried to somehow get me to talk to him about what I thought. About if I really preferred the life I had. And about how he could help me make babysteps. Talk some confidence into me. I didn't see any open paths I could take. Only barriers. Only failures. I remember thinking that I only want to work if I get a really good job. If that's not guaranteed, I won't even try. If I never tried, I never failed. Same with romance.

So it depends on what your stepdaughter wants. Is she moving there against her will? Does your husband have the fatherly abilities to handle this? Or will this just bring conflict and create more anxiety for her?
It does seem that her mother allows her to be comfortable doing the thing she is doing now, which will not be a good situation for change.

By the way, I am not a physics student. In this place I used to add 'top 50' but I am afraid my university had dropped in this year's ranking. But it is still a place where almost everyone is either very smart or every ambitious, or a milder mix of the two. And I am on track to graduate with honours. And that considering I was almost blocked access to normal education after primary school because I was either mildly retarded or had learning disabilities. It seemed in my case a mental health disorder was ruled out.

So education is a strange thing. Becoming an adult is a strange thing. What does your stepdaughter think she can realistically achieve in life? She must have ideas about this. I mean, has she actually given up on the idea of ever being financially independent? I know I have in the past. Maybe very hard to figure out, as it cannot be asked. But do not rule out the case that instead of a lazy teen leeching off parents, she is actually fighting an internal battle. In fact, the two can happen at the same time.