Congratulations!
You've had so much excellent advice already.
I agree about letting her know about your births - I learnt so much about my mum and family history. But don't take it too far. It really annoys me when my mum watches what my son is doing and then lists the age at which me & my brothers did the same thing.
e.g. "Oh look, he's just starting to crawl. Now, how old is he now? He's just coming up to six months, isn't her? Well, your big brother crawled at 5 and a half months and your little brother, well he did everything really early, yes I think he was not quite 5 months, now, I don't really remember how old you were..."
I am sure you would not do this (but then again I am pretty sure my mum isn't aware she's doing it, and would be shocked to find out) but as you can see it can be doubly painful.
So use your wonderful experience to help her, but make it directly relevant to her and her baby, and not to you and your babies (if you see what I mean!)
Have fun!