You of course want to eliminate any physical causes such as teeth needing work or saddle causing pain.
If those are not the cause then you need to look at your equipment. Is the bit too much for her, so she isn't understanding its message? What are you using now and what was she ridden in before?
If you can eliminate all those physical things than you have to look at her training and your attitude. If she is just a little fresh from having so much time off, then nothing but time on her back will help.
If she is just being a snot than that means you will have try not to be a timid rider and not take any crap from her.
My guess is she is just fresh from having the time off. Time in the saddle is your best bet for a cure.
Good luck with her and stay safe.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France