am i being set up for termination and what can i do about it

i work in the medical field and have held my current position for 15 yrs. two years ago I acquired a new boss and it is quite obvious she does not like me. in the first 13 yrs of employment with this company I never received a bad performance review. in the two yrs with the new boss, both reviews were nothing but negative. I am being accused of doing things that just are not true. I honestly believe it is because I am a smoker that she does not like me although I cannot prove this. what are my options, like I said I have 13 yrs of nothing but good and the last 2 yrs bad. I have never been written up, never had a patient complaint against me and never had another employee lodge a complaint against me, yet this boss is saying I am not polite, curtious or respectful to either patient or co workers.

This is eating me up. I don't want to lose my job and I don't like being accused of something that is not true