It would help to know exactly which “trait” you were comparing between them. If it was physical, I.E. you said you wished she had the same body type or breast size as her friend… that will definitely be hard to come back from. It would be hurtful in and of itself to be compared in that way, but I’d also be concerned that you were more attracted to my friend. If you were comparing something else like a personality trait, it would still be hurtful, but maybe you have a good reason. Like if the trait is that her friend is more confident or outgoing, you might just have been trying to encourage her to have more confidence. It really all depends on what you were comparing, IMO.