Which test? the nearest I have found is this:
And the answer correctly says that you can say it. If you saw something saying that 'if i see her i will tell her' is incorrect then it's a mistake.Q20 - If she ..... there, will you give her a message for me?
'if i might have seen her, i will tell her'- This is mixing past and future time and doesn't work. 'Might have seen' would refer to a past possibility of seeing her, so the idea of telling her in the future is illogical. Also, we wouldn't normally use 'might have' in the if clause.