Refreshing "yield to pressure" with 19 year old mare
I would like people's opinions on strategies for doing a refresher of "yield to pressure" with my 19-year-old mare. She definitely KNOWS how to do a turn on the forehand/turn on the haunches from the ground and from the saddle. She KNOWS how to move over on cross-ties when asked with pressure on her side. However, we're in a slump generally with her attitude and responsiveness under saddle, and one thing I've noticed building over the past couple of weeks is her unwillingness to do basic things like yield to pressure when asked (on the ground or in the saddle).
I know I need to nip this in the bud now- I'm looking for advice on what to do when I get flat-out refusal when I ask her to move. Example: standing on cross-ties, ask her to move over with (appropriate) pressure on her girth area, get a blank stare and no movement. She's not being nasty, she's just completely ignoring. But I know that turns into nastiness, hence needing to deal with it now.
In anticipation of some of the responses, I'll say that I don't have a roundpen, and neither this horse nor I have ever been trained in the natural horsemanship techniques (and I don't have access to trainer or mentors with that background). I think this is probably a pretty basic problem that any training philosophy can address, and I'm not bashing or close-minded to different approaches, just saying that realistically, building trust in a roundpen is probably not something that will work in my situation due to my lack of equipment and experience.
I know this probably sounds like a basic question to most people, but this is the first time that I'm addressing problem behavior in my own horse- my experience thus far as been several years of riding broke horses, so this is a new (but welcome) challenge to tackle.