Why does my friend think I one-up her?

My friend has called me a one-upper when I really don't think I do, and if I ever have come across as having one-upped her it wasn't my intention. The only time I say something that is a "one-up" is to try and give her a compliment. She told me I was beautiful and I returned the compliment by saying she's "beautiful inside and out." I was just trying to be nice. Why is she accusing me of one-upping?
Why does my friend think I one-up her?
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