If you are going to run a business, then you need to make sure that contractual obligations are understood and agreed upon before beginning any work. It doesn't matter if you are a horse trainer, ditch digger, or delivery service. You should have a sheet with the terms of your service and expected payment rate and get it signed before you start. Live and learn.

YDI. Firstly because you didn't discuss pricing up front. Secondly because 2 hours is a LOT for a training ride unless you're training for endurance trails. My training rides are 30-40 minutes TOPS, and if an issue can't be fixed immediately, I'll have to revisit it another day (which is very common in the horse world - you can't fix a problem overnight). In the grand scheme of things, this isn't a big deal. There are shitty clients out there who fail to make payments at boarding barns and hay, grain, shavings, labor, facility rent/mortgage costs are VERY expensive. So be thankful you lost out on a couple bills instead of a couple grand.

I've run into this. I've been a personal trainer, and after I give them their assessment, the moment they find out that it will cost them, the client runs out of there faster than they ever would on a treadmill.

this makes no sense to me. it seems like your fee would have been discussed when she hired you. don't you normally tell people ahead of time what you charge? and who in the world would think it was free?

so you never discussed your fee when she hired you? I find that hard to believe.