What are the criteria select a piano teacher?

I just finished my grade 8 Piano with a distinction. I am currently looking for a piano teacher who can teach me Diploma In piano, but first, I know I have to take a Trinity performance certificate before I proceed with either Dip ABRSM, ATCL or LTCL , or ARSM/ LRSM.

What are the qualities that you would look for in a piano teacher and how would you decide ?
I have mixed feelings about proceeding with my current existing teacher. She has been teaching me for about 10 years and I think it is time to switch teacher, but I'm not sure.
She has hinted several times that she also can teach diploma level.If I do go under another teacher, word may get around and she may find out.
Even though I don't quite like her personality ( She has a bad temper) but she actually cares about my career and my grades.
Would it be silly to start from scratch with a new teacher ?