What I would be doing with your Misty, is getting her used to everything. Blankets, hoses, tarps, saddles, ropes, things that make noise, things that don't. Anything that would potentially get her scared out on the trail, or wherever you/she may be.
I would be ground driving her for sure though. As for lunging, that's up to you, I never did it until after my first NH clinic. Now I don't consider my self a NH person, but yes, lunging can help. If nothing else, its something more that's under Misty's belt.
How long have you had her?
For the riding part, just go at the pace YOU feel comfortable with. Granted, if she's turning 10 and you still havent gotten past a walk with her that's a bit extreme.
~The Almighty put hoofs on wind, and a bridle on lightning, He then called it horse.~