How can a 13 year old girl become a Disney channel actress?

You probably can't, but talk to a Disney executive.

However, they don't just hire to "make dreams come true". There are lots of girls who want to be Disney actresses, so only the best actors with the most training can get in.

Or, there's the other route, which is being the child of a celebrity (like most Disney actresses. Miley Cyrus is Billy Cyrus's son, and would probably never have been considered except for her relation to the famous singer)

But for average people who aren't amazingly good actors, and don't have much impressive education and training, it's impossible.