I think that telling these young girls to be prepared for the impact of motherhood is probably a bit like explaining to a 4 year old why they need to look after their teeth - in other words, stuff that happens in your 30's is probably just too remote for them to plan for.
However, I do think she could have been a bit more inspirational and encouraged them to get out there & change the world - after all, if this group of girls can't do it, then who will?
IMO, the key challenges these girls will face are that (1) it often takes till your 30's to establish yourself in a career, which leads to a dilemma about giving it up again so quickly if you want to then have kids and stay home (2) commercial and child-rearing worlds are poles apart, so it can be hard to combine them although that's what most of us try to do (3) as someone else said, the job of full-time motherhood is no longer a lifetime career, and a lack of pensions, risk of divorce, ageing population etc all add pressure for us to keep working and it's v difficult to go back into many jobs after staying at home.
Not sure what we do about (1) but I think we might deal with (2) to some extent if our best young graduates, male and female, insisted on flexible working options from the very start and not just to accommodate parenthood but simply for a better work-life balance. I also think if we could all genuinely have 'portfolio' or multiple careers it would help with (3).
Why can't she be inspiring them to find these sorts of solutions to what is a very complicated issue?