How overweight is overweight?
Girls at around this age tend to have a bit of puppy fat. I know I and my sisters all did at around 12-13 and it all started falling off when I was 14-15. Just be careful!! Weight is such a touchy issue!
f she's eating well, exercises and is happy, I'd personally leave it (unless she's hugely overweight and it's affecting her health).

Good luck with it.
I agree with the above. At this critical age weight is a huge thing for them.

Little athletics in my area was done on a Friday night 7pm-9pm is this something she might be interested in also? If not, perhaps dance like danielle suggested?

It sounds like you are trying your best, and perhaps she does have an emotional eating disorder? Has your DD just all of a sudden packed on the weight? Could her Grandma's passing have anything to do with it?

She is going through puberty, and our hormones are wonderful to us at the best of times (not!) so perhaps it is just puberty?

Good luck with her dad too - I hope he is able to be mature enough to support you in this (by the sounds of it he wont though)