@Earane,
Attractiveness is subjective. There are women that some men may say are ugly while others think are beautiful.
It is stupid and heartless of a friend to say something like that. Obviously you wouldn't. And seeing that beauty is subjective why would you even say that? Did you ask her why she provided that information? Was it under a particular circumstance? Was it that you were dressed average and didn't do much to "perk" yourself up - like it was a sweats/hair in pony tail type of day? Or was it directed overall to how you appear.
There may be truth in what she said because that is her opinion - however, the majority of the world may look at you and think you are beautiful. In the end, it matters most what you feel and how you feel about yourself - that will portray confidence which makes everyone look above average.
I wonder if she lacks confidence - and said such a thing to boost herself up in her mind - otherwise I cannot imagine why anyone especially a friend would make such a comment.