First I was thinking of having her go through the different health issues, and problems horses can have and how to notice the symptoms...when to call a vet....what you can treat yourself and how to treat it.
Then to have me and the trainer (me also due to I've already gone through this process) and take one of the lesson horses or another horse, and pretend to be the seller and the other girls be the propective buyers. We'd show the girls the horse as a buyer would (or should) and answer questions. Also we'd choose some problem...either health problem or attitude problem that the horse will have (won't particularly be a vice/health issue that the horse already has) and we'll try to hide it from the girls...and they have to figure out that we are hiding. Also teach them how to look at a horse move, both under saddle and without a saddle, and be able to tell if they are lame, built downhill, or any movement problems.
And then the basics of how to take care of a horse (more than what we'd do already). Go over worming, shots, and all the other goody fun stuff that horse owners have to do...or at least gelding/stallion owners (health cleaning).
Also, how to tell if a mare is in heat.
What do you all think? Think that idea would be worth suggesting? I don't know about the girls, but I would have loved to have that type of lesson before I started searching for a horse to buy. It would have become handy for me....instead of searching the internet for information like that.