I was and still am very close with my dad (he actually finished Ironman Louisville last year with me) but if I look back to several times as a youth there are 2 comments he doesnt remember saying that truly changed my life (we have discussed these and we're on the page, have come to understanding, etc etc) but were part of why I (in my opinion) developed a body image disorder.
Support your daughters love of running and maybe ride your bike next to her one day. If she has vocalised that she feels too slow to run with you maybe get her mom or a friend to go to the track and jog. Let her enjoy running for the sake of running. These are years that can make and break her relationship with excercise and activity and we want our kids to grow up loving to move!
I think its great you are seeking input on this and looking out for your daughter...but remember men and women communicate differently even from a young age. listen to her when she tells you things and when she cries...If you've ever read Men are from Mars and women are from Venus dont be a 'fixer'. Just listen, explain to her what you just heard her say, and validate those feelings and leave it at that.
Good luck and happy running.