Sorry to hear that you are having problems with your puppy. It's very difficult to assess behaviour without seeing it and you are doing right in getting someone to help you. The only thing I would ask you to ensure is, that they use positive training methods and do not use aversives or talk about dominance and wanting to be pack leaders. These methods have now been shown to be very out dated and in many ways exacerbate problems. I would also be very wary of anyone who talks about "cocker rage". This is a very rare condition and is not a generic term for a cocker showing aggression or guarding issues.(lots of discussion on COL about it)
You say that she growls at you when you take things off her. Do you swap the thing she shouldn't have for things she should have?(something highly prized) If this is the case, an analogy would be if you had something you highly prized and someone came along and took it off you. I would imagine that you wouldn't be best pleased and might have a few choice words to say
Growling is a form of communication.
Has she only just taken a dislike to her halter? Is it the kind that goes round her mouth, as it could be her teeth are really hurting her. If its a harness that goes over her head, try putting your arm with a treat through the neck part, so that she has to put her head into the harness to get the treat. What did you do when she wouldn't let the other dog near the water bowl? and what was the reaction of the other dog?
There are lots of threads in the behaviour section where behaviours like you have described have been discussed. You are not alone and lots of people have been worried about their puppies behaviour. The good news is that the majority of puppies grow out of it, provide they are shown the correct behaviour and boundaries through positive reinforcement and training. Best tip I can give you is reward the behaviours you want and ignore the ones you don't.
Good Luck