I'm sorry, but this goes from bad to worse. You left a gate open and didn't expect her to get out? You seem not to have worked with her, enough to lead her without problems? You don't have a halter which fits properly? You tie a rope around her neck and pull her behind a truck? She falls and gets dragged?
Am I saying this correctly?
If so, find a new, responsible and knowledgeable home for this horse, asap. You and your friend, should not own a horse. Any horse.
You've had her two years, but no halter which fits? You have not worked with her enough to lead her? This is a very bad accident waiting to happen. If there are bears in the area, what difference does it make if the gate is left open?
I thought you were doing well with her, but there constantly seems to be problems and getting worse. I am truly shocked now.
If my little granddaughters, did half the things we have seen here, they would no longer have a horse of their own.