
Hi,
This is an all too common problem, particularly with a dog this age, who has decided the big wide world is
far more interesting than boring old mum! It's called adolescence.
All you can do is practice her recalls, making sure you
never call her when you can see she's going to ignore you. If you call her and she doesn't respond, all you have taught her is that she needn't come when she's called! So only call her when there's a good chance she'll obey, then you can praise her, reward her, and send her off to play again. Don't only call her to put her on the lead and finish the fun. And
never ever scold her when she does come back - dogs have short memories, and she won't see it as being scolded for running off, she'll think she's being scolded for coming back to you, and is less likely to the next time.
Practice in your garden, where she can't run off, and make it into a game. She must be convinced that coming back to you is The Best!!!
I also suggest you buy a copy of The Perfect Puppy, by Gwen bailey, if you haven't already got one. It's got very useful training tips for many things.
Hope this helps. :)