I absolutely do want advice and suggestions on how to deal with this the next time it crops up, so please, comment away! In a perfect world I'd have my trainer come out to work us through it, but it's not an evasion that can be replicated on cue.
Generally, when pointed at a new obstacle that she feels is inappropriate and Does Not Belong, she'll pause, eyeball it, and go backwards if any leg is applied. Whip cues for forwards are either ignored or result in a (small) buck. It doesn't matter if I have contact on the reins or totally drop them. Lateral cues are frequently ignored, though I can sometimes convince her to go straight sideways or back sideways. I can back her past The Obstacle, generally, but try to avoid doing that as a full solution if possible. This weekend, I would back her up the (steep) hill a bunch of steps, ask her to turn and face forwards, and immediately she'd begin backing downhill/off the hill again. I've tried turns on the haunches (doable, as they point her away from whatever she doesn't want to go towards) and turns on the forehand (not very doable, but occasionally we can get that). When this was an issue heading towards the river, I just waited her out. When she was quiet and calm, we'd take one step forwards, and then we'd chill for a bit, repeat. (This is also why I don't start tracking my rides when we leave the barn: it would sometimes take a very, very long time to get to the river.)
If I get off, or if we're following someone else, horse or human, she'll go, not a problem. It feels less like me winning and more like her getting her way when I'm off.
The same behavior surfaces when she really doesn't want to lead: she backs up to put the other horse in front. We've mostly worked through that, mostly by copious leg/whip use when she so much as thinks about it now. Once or twice she did nearly a sliding stop to avoid being in front. That doesn't work for me.
Previous evasions blogged in July 2014 (bag of stuff, eventually followed hikers), earlier in July (putting her sister in front due to coyotes, waited her out?), even earlier in July (putting her sister in front by campground, got off and led), and on my previous primary blog in August 2012 (twice), end of July 2012, March 2012.. our first trail ride ever was May 2011 and I knew backing was her preferred evasion when I started riding her in August 2010. There were plenty of incidents that simply didn't get written up.
So: thoughts? Ideas on what I can try the next time this pops up? Any and all suggestions welcome.