Are you set in having her originate from Bree-land? I ask because a lot of what you describe seems like your character could easily fit in with the Rohirrim.
Though not exactly "magical", many Rohirrim share a strong bond with their horses, going so far as to even have lengthy conversations with them. Sometimes, it is implied that the horses might actually understand what is being said to them, even if they can't effectively communicate back. Unlike Bree-land, Rohan is also ruled by a king, so it would not be impossible for her to have descended from a minor noble house of the Rohirrim, and now serve as some kind of scout or messenger for King Theoden.
How or what she is now doing in Bree-land might be a little tricky, however, and will certainly take some imagination. But it sounds like you have a good amount of that already. Ultimately, I have always found that as long as you play a character well and don't impose upon others, most people won't mind what kind of backstory you've created, even if it isn't 100% in line with what Tolkien was writing. Work with what you've got so far, meet new people and friends to RP with on the server, and build from there. I don't think you'll be disappointed.
[b][size=1][color=green]Raigar - 100 Captain[/color] | [color=green]Raigorn - 100 Hunter[/color][/b]
[i][color=green]Captains of the West - Leader[/color][/i]
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