Tax credits if daughter does not want to go back to college in September

I am in receipt of working tax credits, child tax credits and child benefit for my four children (youngest 8 and oldest 18). My oldest daughter (19 in September) has completed a two-year Level 3 course at college and passed it. She has a part-time college job and was going to go back to college to do another course for a year, until she can find a full-time job where she can use her Level 3 qualification. She now says that she doesn't think that she wants to go back to do another course in September and is going to move in with her boyfriend's family and increase her part-time college job hours (until she can find the job that she actually wants). I've told her that as regards college, she only has a couple of weeks to decide definitely if she is not going back.

Can somebody tell me what happens about the child tax credits and child benefit that I get for her? I realise that if she leaves full-time education, the money will stop. During the summer holidays they continue to pay child tax credits and child benefit as if she is still in full-time education (as they do for children that finish school and will be starting college in September). Term starts on Monday, 7th September, so if she moves out that day and does not go to college, would that be the day that the payments will officially end? Just wondering if she decides not to start on the 7th, if they will ask me to repay all of the child tax credits and child benefit for her that I have received over the summer holidays? Really not sure about this - does anybody know the answer to this? Thank you.