First of all, some people do just have oilier hair than others, so she may be one of them. But I recently went through a period of having excessively oily hair, and I was totally dumbfounded about what was causing it. Changes in diet, hormones, etc. can play a part. Also, I was told by some hairdressers that an overly dry scalp will go into overdrive to produce more oil to moisturize itself, so overwashing, while seemingly the right idea, can actually be counterproductive to reducing scalp oil. I actually posted a question about this... I'm going to link you to it so you can read the responses I got...
This was my first post on the subject:
http://www.mamapedia.com/questions/14077760482475900929
And I posted again a short while later and got these responses:
http://www.mamapedia.com/questions/6838760377149423617
**Especially read MommaL.'s response in this post... it is long, but it really details the essence of oily hair, and what to do/not to do...
Hope you figure this out... my hair has returned to normal... which means that I can basically skip one day of washing and not look like a total greaseball. Hope you can figure this out for your daughter...