My girlfriend wants to dye her hair red?

Ok so me and my girlfriend (Maddi C.) have ben going out six months almost and she has really nice beautiful silky natural blonde hair. And she is about to go off and dye it red like dark red. I dont want her to it is so pretty and I keep asking her and she is so offended! I dont know what to do she keeps saying stuff like my best friend thinks its a good idea it is so frustrating. give me advice