For my dog: group obedience of one on one

Find someone who uses verbal and physical praise - no gimmicks.

Since you are going to have to untrain her (expecting treats for everything she does and only if the mood strikes her) and start again, I most strongly recommend one-on-one until she gets the idea that if she knows the command she does it and she dos it without treats. Shouldn't take more than 3-6 weeks. Once you sort that out, you can join a group class and teach her more than the basics and polish her skills and have her work with the distraction of other dogs.

As for all those who whine "oh,never a slip collar" - well, they obviously haven't done much training or handling and read some books. A slip collar for training is a tool. You have to be taught how to use it - I always put it on the osner's arm to show them how to snap the lead and collar not pull. Works a treat - they got the message fast. (By the way, the ONLY collars allowed in the AKC obedience and agility competitions are slip collar/ chokers and flat buckle, 99% of show competitors use a slip.)