taking in a stray cairn terrier (maybe mixed)

Question
I found a sweet little terrier in the middle of the road. She's not spayed, has had puppies in the past and is in heat. I really love this little dog, would like to adopt it - but it went after my beagle, who attacked back - I got bit in the process. She also went after to nip my shepherd mix who doesn't fight gets along with everyone. The terrier is at the shelter now. They need to observe her for ten days since I got bit. I'd like to keep her - but can she be trained to get along with my dogs. She was okay with my affectionate cat, but one cat went after her and she retaliated. She's about 5-6 years old - probably been homeless for quite sometime. Is it possible to integrate her into my home.

Answer
(NOTE to readers: Caps are used for emphasis and not intended as anything negative.)

This poor little dog has been through proverbial hell.  Who knows what happened to her pups, sounds like she was dumped; life on the "streets" isn't easy and the threat from other dogs can make a stray dog quite fearful and defensive (if that's in fact what happened to her.)  Additionally, she's now in heat.  The dog didn't bite YOU, you got in the WAY (understandably).  You need to be certain the shelter understands this or that dog will be put to death at the end of the ten days as a 'dangerous dog' and unadoptable!  Put a Do Not Destroy on her (if your shelter allows this.)

It's quite possible this little dog is so traumatized, and the hormonal influence may be strong enough, to have caused what may be a total lack of socialization to other dogs (not uncommon, especially with the sort of owner she may have had) and the experience as a stray to turn into automatic aggression.  I can't see that from here.  If you were to adopt her, it would take a considerable amount of time and patience, and a lot of work, to habituate her to your household and other dogs.  Since she "went after" the cat who "attacked " her, this aggression appears to be more based upon high anxiety and hormones; it may not at all mean she's normally aggressive toward other animals (dogs in particular).

My suggestion is put the DND on the dog and start looking for credible rescue agencies in your area.  You can do an online search for "dog adoption", "dog shelters", etc., in your county/state; also go to petfinder.com and do a search in your area to see if there are any bona fide rescue organizations.  Try to get the interest of one of these people (but be sure they're credible, not just some looney tunes who think they're doing it "right").  While none may be in a position to take custody of the dog, you might luck out and find someone with enough experience who will be able to help you determine if the dog can eventually make an adjustment to your home.