Answer: b. would be ugly if she looked her age
Step-by-step explanation:
If this remark is meant as a compliment, it implies that she is better looking than other people at her age, or other people her age are uglier than she is. While this may not be meant to offend, it is possible to view it as a form of ageism.
A less controversial way to compliment her would be to say "You are good looking" without referring to her age. This applies to all form of compliments, including physical or mental agility.