I don't think they were being rude, just real with you, I've been riding for 2 years and I absolutely am not ready for my own horse.
Has any adult got horse experience around you ? Such as parents, aunts/uncles? If so, let them help you guys, if not.. Well, I wouldn't ride the horse until the thrush is better, but start of with basics, rein aids, leg aids, balancing in the saddle, walking, halting, etc etc, depending on if you ride western or English the commands will differ but yeah, that's it.
Also, teach her how to take care of her horse, this is what I would start of with actually, grooming, tacking up, and all that.
Good luck :)
"if perfection existed, it would have four legs & l o v e carrots"