I need help!!
We have a 3 yr old Min Pin that we have had since she was a puppy. We potty-trained her in the apartment we lived in at the time. We used the crate, and she did ok with potty-training. When we moved into a house - it had hardwood floors and she did better there. Then we moved to another state into another house with carpet everywhere!! Seeing that she loved to make on the carpet, we immediately installed a doggie door. She used it often, and made on the carpet when it rained. We assumed she was only pooping, but the other night I brought a black light into our dining room, and it was disturbing. There were so many pee stains hidden in the new carpet that we never caught, it has basically became her toilet!!
Now we don't know what to do. We don't kennel her anymore because we're gone during the day (plus that was the whole point of the doggie door). We can't start using puppy pads or other means now. We take her for walks. We get her to potty outside while we are here. What are our options!!??

If you dont want to crate her, you could block her off in the kitchen. Thats what I do with my Min Pin when we leave. She will pee on my couch. The kitchen floor is easy to clean. Is this house new to you or brand new? The people before you could have left some of those stains?

It sounds like she isn't supervised and trained well enough during her initial potty training. The dog door only works in as far as she is trained to go outside and potty. But it sounds like she never really got the whole potty training thing down pat in the first place, so she's going whenever and wherever she wants. Crate her or keep her in a room with a hard floor surface when you aren't home, keep a close eye on her when you are home, so she isn't given an opportunity to slip up.

If she goes in the house and you catch her in the act of squatting, say NO! sharply, pick her up immediately and take her outside. Keep her outside on a leash until she goes (don't play with her, it's potty time not party time) and then when she does go, praise her and give her a treat. Start going outside with her after meals, after she drinks, etc. Treat and praise her every single time she goes outside, so she learns she gets rewards for going outside.

If you find wet spots or what not and she's not around, then you weren't watching her closely enough. Smack yourself on the head with a rolled up newspaper for not being attentive enough. Clean up the spot with an enzymatic cleaner and keep a closer eye on her. Limit her to only the room you are in, so she won't be able to head to like a bedroom and pee.

If one of my dogs went potty in the house because it rained, he'd be staying outside IN the rain. For a few hours. End of story. You need to teach your dog that she's got to go outside rain or shine, carpet or hardwood floors.