She simply can't change up! (5)
I believe the answer is:
madam
'change up' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'she simply can't' is the wordplay.
I cannot really see how this works, but
'she' could be 'ada' and 'ada' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for madam that I've seen before include "What you would call a female customer (or a spoiled girl!)" , "Titled lady" , "Woman running a brothel" , "'Call Me ---' (I. Berlin)" , "Palindrome used in speaking politely to a woman" .)