I imagine that she was punished in her previous home for going potty in the house, so she made the connection that going potty in front of humans is bad. That's why she waits for the lights to go out or for you to leave the room. Unfortunately, now you have to deal with the fallout of that, but I hope that can give you more compassion and patience moving forward.
First, I would pick up the potty pads. You're going to confuse a dog that is already confused. Clean the spots she has had accidents with an enzymatic cleaner.
Second, don't be afraid to use the crate. It is a tool and I think one that will greatly help you here, especially with a timid dog. Make sure it is the correct size (only big enough to lay down, stand up and turn around in) and make it like a den for her. Feed her inside the crate, have her sleep in the crate. Dogs do not want to eliminate waste in the spots they eat and sleep. Note, this doesn't have to be forever, just until she's potty trained. She will be in this crate when you can't directly supervise.
The next part is going to sound kind of stupid. Do you have a fenced yard? If not, a long line will work, too. Let her get some distance from you, and see if she'll go. If it still isn't working, hide, but still watch. Duck behind a bush or whatever. She doesn't want to go in front of humans, so don't make her. When she goes, just start throwing treats on the ground (try not to hit her poop or pee, haha). I would normally say throw a party, but it sounds like parties scare her, so just throw the treats near her and quietly praise. Or don't praise. Whatever she seems most comfortable with, but I think a shower of treats will get the wheels in her brain turning.
It's probably going to take some time to undo what was done, but give it some time. Set her up for success by helping her never have accidents in he house by using the crate and supervising, and allowing her to potty in the right spot, even if that means you have to hide.
First, I would pick up the potty pads. You're going to confuse a dog that is already confused. Clean the spots she has had accidents with an enzymatic cleaner.
Second, don't be afraid to use the crate. It is a tool and I think one that will greatly help you here, especially with a timid dog. Make sure it is the correct size (only big enough to lay down, stand up and turn around in) and make it like a den for her. Feed her inside the crate, have her sleep in the crate. Dogs do not want to eliminate waste in the spots they eat and sleep. Note, this doesn't have to be forever, just until she's potty trained. She will be in this crate when you can't directly supervise.
The next part is going to sound kind of stupid. Do you have a fenced yard? If not, a long line will work, too. Let her get some distance from you, and see if she'll go. If it still isn't working, hide, but still watch. Duck behind a bush or whatever. She doesn't want to go in front of humans, so don't make her. When she goes, just start throwing treats on the ground (try not to hit her poop or pee, haha). I would normally say throw a party, but it sounds like parties scare her, so just throw the treats near her and quietly praise. Or don't praise. Whatever she seems most comfortable with, but I think a shower of treats will get the wheels in her brain turning.
It's probably going to take some time to undo what was done, but give it some time. Set her up for success by helping her never have accidents in he house by using the crate and supervising, and allowing her to potty in the right spot, even if that means you have to hide.