Don't feel guilty!! I, too, have a Crabbett (Bask/Kellogg) mare who
is the quintessence of rational self preservation (from her point of view).
At six, her gaits weren't half of what they are now at 13, and I didn't
realize then that my communication was entirely too subtle. Even now, after
1,000 miles of long distance competition she'll ask, "Are you SURE we don't
need to check something out back at the trailer??" After I answer MOST
affirmatively, her response is, "O.K., let's get the job DONE."
You may have forgotten the times a few years ago when you had to
stabilize and encourage your older mare! Also, your young mare might be
"beta" and more comfortable following horses (which obviously must be
changed to her being "beta" to your "alpha")
I am now training a seven year old gelding who, with no apparent
effort, just makes the miles disappear. He is perfectly happy to be in the
lead (until something scary appears -- we're dealing with this), never
flipping back an ear for the other horses. He'll cock an ear toward each
side path we pass as if asking to check it out. He is a delight. Sooooo,
perhaps there are, as you say, some horses that take to it naturally.