when we lived in the Los angeles area both my kids modeled and my daughter did a comercial. It is really hard and competitive and you have to be in an area where there is a lot of work. But I would suggest you start by looking in your phone book for agrents and talent managers. Then check with the BBB and make sure that they are legitamate and that they are not schools that are just out for your money. You should never have to pay anything for representation they get their moeny when your kid gets a job. The only thing that you should have to pay for is pictures.
Ebay has started a few child modelling careers. There are sewers who make children's clothing and sell them on Ebay. If you have a good camera (a digital SLR) you can offer to take photos of your daughter modelling the outfits. Most models start out for free and once they become more well known they model in exchange for the outfits. If your pictures are good you may even hear from designer labels. Models who started out this way:
Gabby (in Pickle Juice: http://tinyurl.com/3ru835)
Kristi (in Greggy Girl http://tinyurl.com/4h7wqm )
Chaislyn (in Haven Girl http://tinyurl.com/3wtc9n)
Sophie (in Greggy Girl http://tinyurl.com/3fld4k)
Chaislyn (in Baby Gassy Gooma http://tinyurl.com/4najkx)
Whitney (in Baby Gassy Gooma http://tinyurl.com/4828uo)