There are about 100 ways to go about this. Depends on the horse which works.
First, you could try the "trailer is my resting place" method. Work her outside the trailer (lunging and backing are usually winners). Move her as close to the trailer as you can and have her rest for a minute. Repeat, getting her closer to the trailer every time until she's in. Allow her to rest, back her out, work her, and put her back in.
An alternative is the "out here SUCKS" method. Set her up so she can easily get into the trailer. Have a group of friends put pressure on her from behind in the form of whips (not hitting her; twirling them around), plastic bags (SCARY), and other things that horses dislike. Every set she takes toward the trailer, momentarily stop the pressure. Step by step, she'll get in.
Butt ropes work about 50% of the time. Heavily depends on the horse. They can be used in combination with other methods for an extra touch of pressure that could tip the balance.
If pressure methods make her crazy or just don't work, bribing way be the way. Don't feed her grain in her stall-- just hay and water. Bring her onto the trailer (you said she'd go in for a bite of food), lock her up, and let her eat her grain. Repeat daily. Only feed her grain inside the trailer.
Last edited by Brighteyes; 05-29-2011 at 02:18 PM.