Hi there - I'm sorry for the delay in our response! Sometimes it takes a little bit to find the right expert.
It sounds like you've got a tough situation on your hands. I commend you for taking Gabby on and giving her a much better life than she has had up until you found her!
House training is a frustrating issue when it's not going well, but it can definitely be helped with time and persistence! Do be sure that you've had your vet examine her thoroughly for health problems. If she is having diarrhea, this could lead to more accidents in the house, as she will have a need to go very urgently. Similarly, a bladder infection could cause a pet to urinate frequently and urgently, making them unable to get outside.
In any type of house training problems, I always recommend that we take our pets "back to basics", treating them just as if they are brand new puppies.
There are two important parts to house training a dog: the first is the ‘training’ part and the second is complete and absolute supervision.
Let’s start with training - You can, and should, train a dog to pee or poop just like you can train them to sit. Go outside with your dog, (take cookies!) walk around the yard with them and tell them to ‘go potty’ or whatever word you want to use to teach them to go - just like you’d tell them to sit if you wanted them to sit. When they do go to the bathroom, keep using your 'key phrase' (in my example, I'd say 'good potty!) over and over, then as soon as they're finished, give them the cookie. It's important the the reward happen RIGHT AFTER the behavior (in this case the peeing or pooping). If you wait until they come inside, then all they learn to do is come back inside, not necessarily to pee or poop. Depending on how fast they pick it up, you can have your dog pottying on command within a few weeks.
The second part of house training is the supervision part. She can't be allowed to be out of your sight where she might have an accident. I know this is really really tough, especially if you have kids to watch too, but it's really important that you catch her before the has the opportunity to make a mistake, then give her the opportunity to do the right thing, followed by LOTS of praise. If she's been punished for peeing or pooping in the house before, often the 'take home' message is 'don't pee in front of the humans, they get angry and yell at you' which results in a dog that then sneaks off to pee where you can't see. In order to avoid this, do not punish her if you catch her peeing or pooping in the house - rather calmly take her outside and encourage her to finish. It helps to have them drag a leash around the house attached to their collar so that if she starts to go to the bathroom you can calmly pick up the leash and lead her outside. This is less likely to scare them than you reaching for the collar to 'drag' her outside. Always make sure that once you get outside, you're prompting her to go by using your key words and rewarding her as soon as she's done peeing outside. It's OK to put her in her crate for a short period of time if you're having a really hectic time and can't watch her - as long as she relaxes in the crate and just 'hangs out'.
As a side note, if all the peeing and pooping is happening when you are AWAY from the house, this could indicate separation anxiety. I still do all of the above things with separation anxiety but I also sometimes well consider using anti-anxiety medications to ease the anxiety part.
I sure hope that this helps - please let me know if you have any other questions for me :)