K.B.
First she has to get the ideas onto paper... and then present them to a company to publish them. You can do it by yourself but it is very time consuming so having an agent can really help.
If this would be a younger child books (5-10 pages) get them down on paper, do sketches so that when talking there is something to show. If it is young adult or longer books (over 100 pages) best to have a few chapters written to show.
ABOVE all you need to have started writing something to actually SHOW the publisher so they know what they are investing in. It is very competitive and it is a long process BUT if it is something she really wants to do go for it and don't give up! I have a relative that has written a few books/screen plays and it is something she is pressing VERY actively and it is really hard to get a publisher to give their time to listen even with a fully written book.