I heard about this phrase the other day.

Problem:
The preposition “in” is incorrect.

Explanation:
My friend Nickie F. told me about this phrase.

It seems that someone was telling her about his popularity with his boss.

He said, “Oh well, I guess I’m not the apple in her eye anymore.”

An “apple in one’s eye” is a humorous misstating of the idiom “an apple of one’s eye”, which means a person that one loves very much (FreeDictionary.com).

Good catch, Nickie!

Solution:
“… the apple of her eye …”