i am of the opinion that agents arent needed in this age. i could be wrong as i dont really write fiction. but i am a small press activist , and so i see agents as a hoop you CAN jump through, but you can also just submit work directly to publishers. or publish it yourself.
Getting published has soooo much to do with networking. Look up the Writers Collaborative in your area. They are all over the country and they are working writers that go into the schools and teach. Those people have passion for both young writers and thier craft and if you could find someone like that they would be a great resource http://www.twc.org/
does she have short works that can be submitted to magazines? if she does that first ( or at the same time) she might attract attention to her writing and then make connections. while sylvia plath was a depressed individual and has a sad personal story, she DID submit work to places like Harpers at a young age. So that sort of thing is done. I agree with the previous poster, that depending on the genre of your DDs writing, she should submit it without explaining her age.
but if you are trying to get her into juvenile lit and specialized publishers that publish kids, then of course say her age.
Look into Zine culture. I am not technically a published writer but i have been published a little and i attribute this mainly to my self-publishing adventures with zines ( pronounced Zeen) . I am currently helping to open a community art center and community print shop. I started writing and publishing my own work at your daughters age.
I get all excited when i hear about teen writers. look at www.lulu.com
where she can actually publish herself. you can go into small, local bookstores sometimes and create your OWN marketing , like a cool sign and stuff, and ask if they will sell her book. Sometimes comic book stores are really into helping young writers, depending on how small the store is. Also, even though she isnt in school, maybe an enthusiastic English teacher at a high school could advise you?
Even if she is really talented, is she used to getting critical feedback? cuz she needs to know what it sounds like, how to revise, and how to accept rejection without having it hurt her work ( too much!!!) so i think writing conferences, or writing workshops, or here there are even free writing feedback groups that meet in a book store.. you could bring her places like that !
so i know that was long but i TOLD you i get excited!