Use anti-frizz products... the brand Morrocan Oil, as the other poster mentioned, is an anti-frizz product and adds shine to the hair.
I have that product too, my hairstylist has it at her salon.
Or try finding it online.
Garnier Fructis, also makes good hair products... leave in conditioners or products for adding shine and 'silkiness' to hair... which will alleviate frizz and tangles.
Also, make sure to trim her hair regularly... because split ends, makes the hair tangle, it makes the hair appear 'dry' and it will look frizzier. And if split ends are not trimmed off, it will split up the entire hair shaft... making the hair in worse condition.
I would also HIGHLY HIGHLY recommend, from Sephora, the "detangling brush" for hair. I have it for my daughter, and it really works well... making the hair very nice and getting out tangles and frizz. It is well worth the price.
Here is the link:
http://www.sephora.com/browse/product.jhtml?id=P241318&am...
good luck,
Susan