Newquay. You are a very loving and caring Grandmother.
I think you are right to be concerned because it is best to notice one's children and grandchildren and think about their well-being than to just assume that they are OK. She may be fine. She is quite likely a quiet girl who enjoys reading and doesn't notice the time passing by. For all we know she is on the internet with a boyfriend met at university and the time is flying by.
But you need to just gently and unobtrusively make sure she is happy.
I think the best way is to be open. If she knows you well and knows you love her and only want the best for her, she will understand if you simply ask her if she is feeling ok. You could take her out for coffee and a bit of shop browsing (maybe she can help you choose something you need). Then ask quite directly and very kindly how things are going. Tell her you are a bit worried. Is she lonely? Does she wish there was more to do in the holidays? Make absolutely sure she knows you are not prying into her private life and you are not there as a spy for her parents.
Doing well in her exams is not a guide to whether a student is actually enjoying university or school. I know a student who won many awards but attempted suicide. She was being bullied. Possibly because she was so clever and not the most social kind. She was shy and nervous around the very confident party-animals which appear to predominate among the student mix. They are not the majority in fact but just the loudest and the ones who say the cruelest things. I would try and encourage her to feel relaxed and confident enough to tell you about university life. You can say you can't really imagine it and would love to know, or it was so different in your day.
I am sure, that having noticed her quietness and how she spends time indoors alone, and being worried enough to write here, that you are the ideal sensitive person to approach her. You might well be far better than her parents for this. Sometimes it's very hard for a young person to open up to parents. They do not want to upset them and want to make them proud. A kind granny with a gentle manner might be a real blessing to a highly intelligent girl who is feeling upset.
I am not saying she is upset! I am preparing for the 'just in case' scenario!
I do hope your DGD will turn to you with a smile and say she his fine. But should she be feeling low, I think you will be the perfect person to put your arm round her and tell her how important to you she is and that she can tell you anything she likes.
If you find out that she is depressed, then you'll need to see that she sees her Doctor. Also that the Mental Health Services at the University know and are ready to support her. They can be excellent. So in case. she needs help, be prepared to support her this way, which I know you will. Also to tell her how very normal it is to feel depressed especially when you're at university!
Once again, I'm only saying this in case that is the situation! I hope she is fine and just taking a well-earned break! That would make complete sense too!
I wish you and your DGD much happiness, and good wishes for your chats with her. She's so lucky to have you! Take care of yourself and her! Elle x ? ?