Oodles (and others) offer very good advice but I do totally sympathise with your own feelings.
Currently both my 2 AC are struggling for completely different reasons. Like you I live a long way away (in another country actually) and have just been over for a pre-Christmas visit. I so looked forward to spending time with them. We are an affectionate and supportive family. But, in fact, I spent both visits shopping, cleaning, cooking etc (which I was happy to do) and hardly saw them because they work such long hours and were so tired and often fed up when they got home.
My DD is having counselling and I too spend all the time hearing her go round and round in circles of sadness and worry. I can only listen, listen, listen and console and cuddle her and then go to bed (or home eventually) and cry myself.
One understands that 'help' and 'advice' can be seen as patronising and unhelpful but sometimes I run out of 'oh dear' and mmmmm and other hopefully reassuring noises. I come away feeling anxious and helpless (and a little frustrated too!) but usually my daughter texts me later and thanks me for listening.
On the other hand, my own mother who was a kind soul, discouraged all conversation about sadness or difficulties as she herself found it too upsetting. This meant I bottled up everything even when going through a divorce with 2 young children and, in some ways, I don't think I ever got over that feeling of suppression.
So I offer a ((hug)) to you. And very much hope your daughter sees her life more positively soon.