It's so sweet that you want to get her something horsey related! I would ask to get detailed descriptions of what she wants. Horse things are very specific and it is hard not to get something wrong if you don't know exactly what you're doing.
QUICK CRASH COURSE ON HORSES (Or QCC). So you can understand when she talks to you about everything horse related AND impress her with your knowledge! (I know it can sound like horse people talk gibberish sometimes).
PARTS OF THE HORSE: http://horsewise.files.wordpress.com...ody_parts2.gif
Which ones you hear a lot (that aren't obvious): Poll, dock, withers and frog (which is the triangle shaped area inside the hooves).
"Tacking up" is putting the saddle, bridle, etc on the horse.
"Grooming" is brushing (etc) the horse.
Walk: Obvious. Slowest, four-beat gait.
Trot: Faster than the walk. Two-beat gait. Legs move in diagonal pairs. English riders mostly post (move up and down with) the trot while Western riders mostly sit the trot.
Canter: Faster than the trot. Three-beat gait (correct me if I'm wrong). Smoother motion than the trot normally.
Gallop: Fastest gait. Horses have been known to go an excess of 50mph here. Forget how many beats it is.
"Gait" walk, trot, canter and gallop usually, though certain breeds have extra gaits.
BASIC HORSE BEHAVIOR:
*Ears pinned back: Aggression. This horse wants you out of its space. May be preparing to bite/nip.
*Tail swishing (when not fly season): Annoyance/impatience.
*Stomping hooves: Impatience. (Horses may also quick out a bit and stomp if the flies are bad).
*Head bobbing: Impatience. May also indicate lameness.
*Cocked back hoof: May be a warning that the horse is about to kick. This generally does NOT look the same as a leg that is lifted in relaxation.
*Swinging hind quarters toward you/generally not respecting your space: This is disrespectful and may indicate aggresion if coupled with ears pinned back and other aggresive behavior.
*Always remember that a horse is a herd animal and behaves like one.
There is a LOT to horses! I strongly encourage you to read up on them. Even if the romantic relationship with this girl doesn't work out in the end, you may end up loving riding yourself!
Random gift ideas because I'm bored (note that I ride English):
*Coat (especially if you live in a cold climate, like I do!)
*Polo (especially if the girl does fun shows)
*Paddock boots (ankle-length)
*Tall boots (she'll need to be measured specially for these, though)
*Horse treats (apples, carrots, and peppermints work)
I don't own a horse so my list is fairly short just off the top of my head. I'll edit if I can come up with anything else.
Good luck and I hope I helped!