Describing Katy with only 3 words would be very hard. Before I seriously attempt it, I have a question: would we be describing her to someone with no knowledge of who she is, in which case we'd have to use "singer" as one of the words, so that they know she's a singer? Or would we be describing her to someone who knows she's a singer and is vaguely familiar, in which case we could use 3 adjectives?
Obviously "beautiful" would have to be one of the words, since absolutely everything about her transcends beauty: her voice, the songs she writes, her looks, her personality.
And of course, "inspirational" would have to be one of the words, since her backstory and her songs are both inspirational.
The word "conflicted" could be used (and I do not mean that as a negative) since she feels a conflict between being a "good" Christian girl vs. a "bad" girl, and that is sometimes a topic of her songs. Maybe "contrasting" would be better than "conflicted", since it sounds less negative, though I think Katy herself would be fine with "conflicted".
In fact, even to describe her voice, I would need an even number of words to describe the contrasts. Her voice is so soft yet so strong, and so sexy yet so sweet and angelic.
Again, if you answer whether or not we're describing her to someone who already knows she's a singer, and I'll either way come up with 3 words. Obviously "beautiful" and "inspirational" will be 2 of them.