I have kind of similar issues sometimes. I'm in college, and school's about an hour from home. I get to come home most weekends, but between being gone (sister takes care of the horses, but she's got a lot on her plate, too, between high school and a part time job) and the nasty weather and footing I don't get to do much with Scout, and he doesn't get to go outside like he does in the other 3 seasons. I hate making excuses for it, and I spend my weekends and breaks bringing him back down to earth, but the culmination of all the "winter stuff" takes it's toll on his understanding of manners in general. As of now, he needs saddled and put onto a forward trot until he offers to walk, but my whole farm is a slippery frozen wreck...
get better as the weather breaks, I'm sure of it. There may be a little "spring fever" time, but by and large she'll likely improve. For myself, I resign myself to a 3 month riding hiatus, and spend about the first 3 rides of the spring reestablishing sanity and the stuff he knew in the fall, and we continue on our merry for the summer. I do like SeWHC's idea of just going back to the walk and trot under saddle, reestablishing sanity and respect there. It sounds like you've got a good handle on things on the ground, which tells me that it shouldn't take a lot to convince Chance that you're still worthy of respect in the saddle.
Good luck, and ride safely! Things will get easier, I'm sure of it!