For ongoing games, we leave it up to you to decide how she contacted. For example, she could have simply used a private message feature if the game has such a thing with an offer to work for her in exchange for paying off her debts and returning her home with a wish. That's only an example of course!

As for the form, if you wish for her to be able to keep her horse form, she may, though it will certainly limit her to certain jobs (some spirits may take a liking to her however). The Witch will probably ask her to be human but if she displays a strong preference she doesn't really care if her worker is human at the end of the day. Should you wish to switch forms at any point we can probably figure out something for that too!