I am 5'5", very skinny (though I do have a butt, and 34" hip measurement)with a 32" inseam. I've got problems with pants as well, many 0s in women's stores are two big, a 14 in kids great but is too short, a 16 is usually too big.. and sometimes too short as well! Plus I have skinny legs and small waist, so if it fits my hips it bags everywhere else.
I recommend Pacific Sunwear, they are two pairs fo $55 and their size chart online is quite accurate. I was a 00 there when my hips were 33", now I'm more a 0.
http://shop.pacsun.com/content_popup...ame=Size_Chart
is she very tall? Does she need extra-long pants? My sister is 5'10" with 34" hips and a 34" inseam.. I could ask her. I know she has several pairs of 00 pants from American Eagle that fit well, they offer many different inseam lengths.