Dominant cocker spaniel puppy

Question
My 13 week old cocker spaniel puppy (bitch) is generally great, she has been house trained for weeks, she sleeps well and plays fetch amazingly.
We have a couple of problems with her dominants, she has become very dominant, snarls, growls and jumps up at me as if she is going to bite showing her teeth when she doesn't get her own way and we have tried everything from getting down to her level and staring in her eyes saying no, too taking her away from situation to play to spraying her with water but nothing seems to work or bother her. She also howls
When left on her own, I've tried building the time up and setting up a game of hide and seek with treats but I cant even leave the room without her crying.

Can you help, what am I doing wrong. I'm worried she is going to grow into a angry dominant dog rather than the obedient, respectful family dog we want and need.

Answer
When she puts on this show and you get down on her level (sit on the floor) saying NO and staring her down, it can sometimes take a minute.  The key also is to be physically very still and to keep your voice calm but a bit threatening.   Keep saying NO.. And never lose eye contact.

You need to keep this up until she breaks eye contact.  You just won.

As to the separation anxiety - where is she when nobody is home?  At 13 weeks she needs to be confined in a safe place.  Where does she sleep?  How long will she keep up the ruckus?

Don't panic - she's a baby and is trying you on.  Now is the time to correct this and first I want to be sure you're doing the 'staring down' bit right.  If that doesn't work we'll move on to something a bit more unpleasant (but harmless).