This definitely sounds like ulcers. How recently did you treat for ulcers? Was it treatment following a diagnosis or just treating just in case? Did the treatment seem to help her behavior? If so, did the behavior return after treatment was finished?
I think (if she DID have ulcers and DOESN'T anymore) that she might have been saddled and blanketed enough inside to associate the pain with the saddle and blankets in the indoor environment only. Either that, or she's distracted enough when she's outside to not notice the tack as much.
If you haven't had a vet out yet, I would definitely consider getting one out, ideally one that is experienced/trained enough to recognize any body pain that may or may not be ulcer-related.
Is there any issue with tacking and riding her outside more often? If that's where she's happy, that's where I would do my normal daily routine with her. Yeah, I know, I know, inside is more convenient in bad weather and horses should get over it and training should correct it - I've heard it before, may or may not agree on some of those points - but honestly, if it really makes her that much happier, why not?