Why do you ask why someone would give a Paso Fino to a new rider? I'm no expert, but the Paso Finos (and Peruvian Pasos) that I have known have been terrific horses - very smart, playful and more people oriented than horses are generally.
I think you're smart to do a lot of ground work with her at first, even without her health issues. There is a lot more than just lunging - teaching her to pay attention to you as you lead her - will she tune in to your movements enough to turn without a signal, stop when you stop, match your pace? Does she know how to yield her hindquarters? There are the Parrelli 7 games, Anderson's lunging for respect, etc.
There's also some good books on stretches you can do with her that might keep her "in" better once she's been adjusted. I'm sure your chiro can give you some as well.
BTW, once you feel like you are ready for it, bareback is an excellent training tool for developing your seat. If it makes you nervous, you can do it at first with someone else leading her for you, but it sounds like she's probably a good horse to try it with. It also takes the saddle out of the equation.
Last edited by Pagancat; 09-03-2014 at 07:40 PM.