Starting a horse over jumps?

I'm thinking about taking my mare the hj route. She really loves jumping, I didn't even buy her for this purpose. I figured she would be a good broodmare and possibly english pleasure show horse. About a month after I got her (late July) I was longing my old jumper Anglo Arab over some 1' ones because he likes to work. He used to jump 3' plus in the ring and I've seen him clear much higher than that in the field, but he's nearly 20 and just isn't up to it anymore, so (even though he hates it) I make him go over the lower ones. She was watching him closely, not grazing, just sitting at the edge of the paddock looking at us. As I wrapped up working with him, I led him over to the water trough only to hear a horse somewhere going at a fast canter. I looked back over my shoulder and she was repeating the same circle my gelding was doing, and going over the jump like it was nothing, and she was having a complete blast. It was even cooler to me because I knew that this was the first time in her life she had ever been able to jump over anything!

Harper, the mare in question, is a Tennessee Walker and was rescued from a soring barn back in June. Until she came to me, she had had performance pads on since she was 2, and had never once been turned out. For more info on the torture these horses go through, please visit Walkin on Ranch. I was worried that because she had never been out of a stall, and had flipped out a little when I went to visit her, she might be a tough case to handle. Turns out, her one and only vice is that she is impossible to be around when she's hungry. She will eat anything, and in the case of her former residence, that was her stall door. She had literally eaten half of it and has the teeth now of a horse much older. Now that she is being fed as much as she needs to be, she is the sweetest puppy dog of a horse I've ever met. She learns so fast I have a hard time keeping up!

I have been working her over 6" to 1' jumps at walk, running and flat walk, and canter, just as I have my old guy. But she just walks over these, being a full 17.2hh and him at maybe 15.1, and half the time doesn't even bother jumping.. How do I gauge what height she needs to at least keep her from walking straight over it? Just keep raising it until she has to jump? And what increments do standards jumps go up? I heard from one person it was 8", but I'm double checking. She is being longed right now because I am giving her a break from being ridden, but I get the feeling she will have me and a saddle on her back soon.

When I do get up on her, and give her some time of getting used to a rider without her wearing those awful shoes, how should I begin training her to jump with someone on her? What is the best way to find a good trainer?

Thanks for any advice given! If I left an important piece of info out (which, knowing me, I did) just ask and I'll respond with it! And for the record, yes, you can jump a walker!