It is time to be assertive with her. Remember the 3 part assertiveness statement
"when you (observation), I feel (label it), desired action (such as please stop, or 'can you please be more positive'). Often a bit of assertiveness is enough to pull things back on track. You might find that it starts a conversation about different things that you can both work on, or it might highlight that you have different values and shouldn't bother with each other.
Are you scared to tell her that you don't like her?
I hope things work out for you.