If she had told me that being a parent is the hardest thing in the world and we all get it wrong sometimes, it would have helped. Not so much then - but now as I try hard to be a good enough mum - not a "perfect" mum to my daughter.
I wish my mother had told me that I could be anything I wanted, if I wanted it enough. Instead I was encouraged to play safe with life and work, whereas aiming for the stars and possibly reaching the tree tops is a better way to live. I wish my mum had been able to admit that she wasn't always right, or didn't have all the answers, just because she'd had more birthdays.
I wish my parents had not made out that sex was such a big deal, as it was for their generation, and that saving myself was all that mattered. Or they'd look worried and warn me that boys would get carried away. I never understood that, and still don't.
But they were doing their best.
I am still learning what to tell my daughter. Unfortunately, I am a very controlling kind of mum, so I tell her what I think a lot. Too often. So, I took a few soundings from my friends to find out what they thought and this is what I discovered.
All 18-year-old daughters should be told they are gorgeous - because they are. As Hazel said, "I wish I'd been told how great my legs were then, because I didn't know it." They have dewy skin, firm upper arms, and waists. So that's a reminder to me that I must continue to tell my daughter that her long, shiny, hair is gorgeous and please don't cut it - yet.
Don't rush to grow up too quickly. There is plenty of time to settle down and take on responsibilities, because once you have, you can't turn back the clock. Whether it's partner, a child or a mortgage that ties you down - there's no hurry.
I should tell my daughter that no man is worth crying over - because if they make you cry, they are simply not worth it. The same applies if they play games and are not that into you. And as someone suggested to me, "Never run after men or buses." Because in either case there will be another one along in a minute.
And wait for the right man - don't compromise or settle for someone who's just okay, because all your friends are in relationships.
I'll advise her to push the boundaries, take risks and live every day to the full.
I'll tell her that just because I am older, it doesn't mean I have all the answers. In fact, the more I know, the more I realise how little I do know. When I was 20, I saw the world in two shades: black and white. Now it's mainly grey.
I'll tell my daughter that because I love her, I'll always err on the side of protecting her from life's knocks - but that she may need to remind me that she needs to make her own decisions and, perhaps, mistakes.
I'll tell her that she can have the benefit of my experiences in life, but that she doesn't have to listen to me, because she is not me.
But maybe the one thing I do have to instil in her is the sense to have confidence in her own decisions. Because I am a bossy, controlling, know-it-all mum - and we all know that mums are always right. Aren't we?