My 14 month gsd has started to be more aggresive ?

Basically my gsd is about 14 months old and she is fine with me and everything but recently when i have taken her out she is more aggresive towards over dogs . But its only when shes got her stick when i throw it and she brings it back and another dog goes up to her she will just keep avoiding it and then she just switches she has never bitten just growls and like chases them with her mouth open . I was wondering if its the food im feeding her i used to feed her 1 tin and 3 hand fulls of biscuits one in the morning then the same at night . But recently at both meals i have been mixing raw rabbit , raw tripe etc but its from pets at home . Is this what could be triggering her because it still has blood in it ? Or is it some thing at her age . She has been sprayed .Thanks