Agility conditioning

I really like swimming for conditioning - is that option available to you???
 
Walking with speed intervals (or constant trotting/jogging as your dog gets fitter) on a soft surface is also a good idea.  I prefer to do this with my dog off-leash in the fields  so he can set his own pace (which is usually much faster than mine).  Hill work is also a great way to buil muscle/stamina. 
 
Dodger is big enough that I use weight pulling/carting as a way to condition him. Whenever we practice, I rarely have the jumps at full height, especially when setting up cavelletti's (for fitness, accuracy and scope).  I use sit pretty (the beg position) as a strengthening exercise year round as well as a weighted doggy-back pack.
 
If you don't already do so, part of conditioning is stretches IMO... I have Dodger do stretches as a warm up and cool down before most strenuous activities - some are on command like bow, others I have to manipulate him into doing.
 
Have fun![]

I do a really mixed set of stuff-- off leash hikes over rough terrrain are probably the best general conditioner. Steady trotting on leash is great for endurance. To build speed and an explosive start you can do "speed circles" and sprint drills. Tight figure eights around poles or trees are good for building speed on the turns. For hind ends, "dancing" the dog around on the hind legs, doing slow controlled descent on ramps, walking up hills, jumping grids, and weight-pulling. Rocking the dog on a rocker board or exercise ball can build a good core. And nothing beats swimming.

Thanks Guys!!!
Lots of great ideas for me to start and give her a variety -she gets bores so easy.   Will definitely add swimming in the spring   - Minnesota land of 10,000 lakes..  frozen right now [].
We have been doing streches (circles & stuff).  I am very excited about us doing agility, but have to remind myself to be patient it doesn't happen overnight, especially since we are both learning.
 
 

Also try some exercises for improving her back-end awareness, like teaching her to walk backwards, and having her walk across bars (eg. walk along a ladder).

We built up hind leg awareness by having the dogs stand on something with their front legs, then only move the back legs around it in circles in each direction. Anything will work for this, you can turn over a dish, or put a book the floor, it really doesn't matter. You may have to walk into your dog a bit to get him/her to move around, but at least for Max, once he realized what it was I wanted him to do (I did use a clicker) he started taking a few steps around in each direction on his own. I also took the half exercise ball thing my dad had (it's half an exercise ball on a platform thing so it has a flat bottom) and had him sit and stand on that. I started this because he was driving me nuts one night while I was trying to watch tv, but this really did well for working on his back legs (though I think those balls are too expensive to buy one just for the dog). 

Peak Performance: Conditioning the Canine Athlete
 
If you really want to do it right, plus have an excellent resource on structure, nutrition and rehab.  this is the book you want.
 
Written by Chris Zink DVM  who is  a sport competitor herself.  If you ever get the opportunity to go to one of her clinics, do so...Well worth the money.