What breed would make a good companion dog for a 1.5 year old female ACD?

I personally feel one should get a second dog because one wants another dog, not as a companion for a dog one already has. Decide on the kind of dog you want, and then see whether your dogs are a good fit for each other.
I'm hoping the fence has been fixed
http://www.dogforum.com/introductions/seems-like-queensland-heelers-spirit-broken-290825/

Thanks for your reply. No, the electric fence has not been fixed. It still shows that there is a break in it somewhere and I haven't been able to find it. (5 acres) But I'm not planning to get another dog until I get the OK from the Vet on the Valley Fever situation.

I have brought two dogs in the past. A Miniature Dobi and a Corgi and Lady got along with both of them very well. (Not at the same time.) But eventually both of them slipped under the existing fence which is why I started installing an electric fence. It's not really electric. It gives off a correction in the dogs collar when they get too close to the boundary wire.

As someone who also has a female ACD mix, I have to say that the best companion for he would be a dog that she gets along with! In my experience a lot of ACD mixes can be er...selective, bordering on nasty with some other dogs, and they can be a "sheriff". I think you should see what dogs at any local shelters that you like and then see how your girl does with them. Typically the best combo with a female (esp with a pushy one, if yours is) is a male that's smaller or younger, or at least with a wimpy personality! But who knows who your dog will click with.

Thank you for your reply. Lady is very laid back and wants to be friends with everybody, humans and dogs. We live in the Sonoran Desert and the only thing that gets her going is horses and flying vultures or hawks.