I'm unsure whether you're refering to Geraldine McEwan who is the new Miss Marple on ITV or Joan Hickson who played the role on BBC.
I think it's the latter you're probably refering to.
Actually I quite like her but I'm not sure about the unfaithful adaptations that she appears in.
The Joan Hickson adaptations were more faithful to their source material but I felt her interpretation of the character didn't really bring out Miss Marple's formidable intellect.
There again I felt the same way about Margaret Rutherford & I still have a soft spot for her.