I'd say try to stick it out, but if she marks you unsatisfactory (or some equivalent of it) for your clinical, then consider asking for a different instructor. If another instructor shares the opinion of your current one, then it's just you. I, however, would be surprised if this is the case. There's a wide variety of clinical instructors out there.
Some clinical instructors are frickin' awesome. I have one now that makes me "wanna be like her when I grow up". She is simply an amazing nurse and has high expectations and loves to teach others what she knows. She doesn't make you feel stupid but encourages you to be excellent and "make her proud". Some other instructors, on the other hand, should be barred from having contact with human beings. I've have been in school studying different things for quite some time and have never seen such a oddly wild spectrum of instructor quality as I have in nursing school. I have no explanation for it. At any rate, I recommend sticking it out. Try to excel and if you truly think she's giving you a raw deal it can't hurt to ask for a different instructor (you may not be granted this request, but it can't hurt to ask).