It makes sense to feel that way, especially if you struggled when you left home and felt like your mother wasn't there for you. Survivors often go through the old traumas again when their children or someone else close to them is at the same developmental stage. And I think that letting go of your first and your last child is recognized as being pretty hard for parents anyway.

This is different from when you left home though. You aren't your mum and your daughter isn't you. You can be there for her and also allow her to be strong on her own. Take your lead from her now, but let her know that you love her and still want to be there for her when she needs you.

I haven't had a child leave home yet (my oldest is 16), but I remember when I left home all too well. I was the oldest, and my mother didn't know how to let go, so it was a battle to break free, with abandonment as the result. Leavings can be very traumatic, but they don't have to be. You can leave the door open.