It sounds like she may not even be bothered to apply to uni, which could be a good thing, as she will have an enforced gap year after A levels. You just have to be strict about her not lazing around during that year, she has to work/volunteer etc.
I have an immature 18yo, finished BTEC this summer, not sure what she wants to do at all, or even if she will go uni. We all agreed that a gap year would be the best thing - she has a PT retail job that pays reasonably well, lots of overtime, and is sorting out some local volunteering at present, plus is a young guide leader.
Her plan is to do some volunteering/travelling abroad from next summer, once she has saved up money (currently finishing paying off her car and insurance, then moving on to travel fund, does have a social life but not excessive). So it looks like a gap year may turn into 2 years, but as long as she is doing something there is not much we can say. No point pushing her into making a decision about future career too early and she has said that she hopes volunteering may help her in decision making. She can laze around like any other teenager, but is generally off when I am at work and does help in house and with dog walking.
A friend from work has a DD similar to yours. Grammar school, v good GCSEs, was originally predicted v good A levels but that has changed as she now has a job and social life and studying seems to come a distant third. My friend is panicking that her DD isn't sure what she wants to do, isn't sure she will stick uni and apply herself etc, but is pushing and pushing her to do PS. I can see her DD being turned off applying this year, and I have tried to suggest a gap year, as per my DD, but my friend thinks thats only ok as long as she still applies this year.
She doesn't seem to want to take on board - let her do A levels and apply next year. She thinks she wont apply. I have tried to reason with her that 18yo have to make up their own mind, we cant make it for them. I have learnt that from my DD!!!
I do think there is too much pressure to apply in Yr 13 and go straight from A levels. I have a few friends like my colleague, who think they must go at 18 and who quite clearly look down on my DD for not currently being at uni!!!!
But I also know a few who have gone after a gap year or 2 and are thriving. One is a uni housemate of my DS, she was almost 21 when she went, having had 2 yrs of travelling and working, and the difference in maturity when sorting out their shared house was very obvious. She very much took the lead.