Remind her to love herself more.

 

When she loves herself, that "self" becomes more lovable, because she has less need for love from others, who in turn feel less burdened subconsciously.

Her shyness indicates the "self" not getting adequate cover by her own love and needing reassurance from others, who may not know or care.

She has plenty of time to work on loving herself first. That self-love may be intoxicating to boys, because the love they offer is different.