I've been cutting my hair since I was 16 and I've always kept a fade and had the barber round out the back of my head. Sometimes I'll have it lined up because I hate my widows peak.
Like @KneeGrow. said though it also depends on the face/head shape and body as well.
Depends on the face shape and body type
Need pics to determine
A lil taper would look nice with waves. Depending on how her hair grows a soft line may be recommended. Stylistically it depends on the barber you go to.
Her face is round.
Her face is round, thick body type.