Seeing your child dealing with loss is the hardest. In my case it overrode my ability to deal with my own grief. Eventually (glossing over the irrelevant details) he came out the other side, and is doing fine. And once I didn’t have to spend all my emotional energy on him I could look after myself.
Your daughter is 17 which may give you additional concern. My child was a few years younger but he missed all of that stressful middle-class “get the right classes, right prep and right scores”. It was simply not possible except a bit of going through the motions. But in the end none of that mattered and he ended up in a place where he probably would have been had he gone through those stressful gyrations. So my unsolicited advice is: if you can manage to support her in stepping off the treadmill and dealing with whatever is the highest priorities for her, she’ll probably ultimately be fine.
There are unfortunately no guarantees, but many people do make it to the other side, however horrible the path may be.
A friend of mine lost his wife a few months ago (she had really stepped up to help me). His three kids each reacted completely differently and I am amazed at his ability to accept the needs of each one.