Unfortunately, kids (and if we're being honest, adults too) feel so much pressure from their friends and how people perceive them.
If you're someone who lacks self-confidence or has a strong desire to fit into a certain group (something to which I can unfortunately relate), it is hard to alter that mindset.
My only advice would be to sit down and have a heart-to-heart with her and really find out what people are saying, what she doesn't like, what she would change if she could so you have a point of reference for where she's coming.
It took until after college for me to be genuine with myself about who I am and who I want to associate with personally. Hindsight being 20/20, there's so much I would change about my upbringing, but it took that experience, the trials and tribulations to get here.
The honest truth is that our world is very image conscious - many people do get passed-by for jobs because they aren't pretty enough or popular enough. Keep pressing on her to be authentic to herself and find what makes her incredible and unique so she can thrive in any of life's challenges.