Hi there,
I am 32 and I have stammered since I was about 9 or 10. I haven't got a severe stammer, but it has effected my life a great deal. Sometimes I control it with no problem, and I almost forget about it. A lot of the time, it's there though - it flares up when I'm stressed, worried, under pressure etc and my one big problem is speaking on the telephone - that's my mental block. School and teenage years were the worst really, because of just being a teenager, I suppose - it's a very self concious time.
I went to university, I have a husband and three children, my life is good. However, the area that it has effected is work. I've only ever had "easy" jobs. I deliberately avoided having a career I suppose. It's easier for me to be a housewife and a stay at home mum.
The main difference now, from when I was 15, is just that with age comes confidence. Yes, I have a stammer, but it's not the end of the world, and I have acheived what I wanted to in life. When I was 15 I was very worried about my future, but now it's okay. When I was 15, I was mortified if I stammered in public. Now, I just find it a nuisance, say to the person, "I'm sorry, I have a stammer" and that difuses the situation, and it's fine. I'm not embarrassed about it any more.
I'm not sure if I have any advice for your daughter - just that she should concentrate on the things she CAN do, rather than worry about the things she can't do. And that as she get's older, even if the stammer doesn't improve, her attitude towards it probably will. She will become more at peace with it.
By the way, if you think it's exhausting watching her stammer, it's 10 times more exhausting for the stammerer.