How do I compliment her personality?

So my girlfriend is a very beautiful girl and I tell her often how pretty and gorgeous she is, but she's worried I only like her for her beauty. When we first started going out I wasn't physically attracted to her, but she was really sweet and had the best personality and over time I realized how beautiful she is. But complimenting personality is harder than complimenting physical appearances so is there anything I can say?
How do I compliment her personality?
Post Opinion