Hmm ...
That is a stumper.
It's certainly not THE UNINVITED, and while there are several films titled THE UNINVITED GUEST, none fit the description. There's a haunted mirror sequence in DEAD OF NIGHT, though that doesn't seem quite right either. Could it have been a Mexican film? Check out THE WITCH'S MIRROR. The plot is completely insane, but the imagery is plenty nightmarish enough to have made a lasting impression (i.e., a delicious warping effect) on a young mind.
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