Horse is started to get irritated while riding?

I know what you're going thru, my 4 year old paint acts like that at times. Definitely go back to groundwork, the stubbornness can either be from not understanding your cues or she doesn't respect you and is being lazy. Try the lunging, then go back to riding and try again. If she still resists, try going back to something else she knows and work with that for a while. Also remember that horses have their bad days, so she just might be having hers. Or it might just be a mare thing.