Introducing dog to muzzle

My 1 year old recently started getting into trouble at the dog run and last week had a nasty incident and really injured the other dog. I had been working with a trainer and want to continue socializing my dog - especially because she seems to really need a lot of social time - but I don't feel safe taking her back in without a muzzle. Does anyone had any advice on: a) what kind of muzzle to buy and b) how to introduce/train her to play with others while wearing a muzzle and be happy about it?