scold her when she doesn’t
is why she does this
hides under the couch after she does.
Dogs do what is safe and what is effective. She has learned that you don't like seeing her urinate/defecate in the house, so she avoids you. That avoidance could very well be why she is hesitant to use the pads.
First thing I would do is suggest taking her to the vet to ensure there is no health problems going on.
Second, treat her like an 8 week old puppy. After she eats, put her on the pad. After she drinks, put her on the pad. After she plays, on the pad. After she wakes up, put her on the pad. And then failing all else, put her on the pad every hour. (Or if you want to change to training her to go outside, replace the pad with being outside). Keep her on leash in the house, tethered to you or in a confined room. I wouldn't recommend a crate since she doesn't seem to have a problem sitting in her own urine/faeces.
Make it a huge thing when she goes where you want, lots of praise, treats, toys, whatever her favourite thing is.
Some dogs do struggle with potty training. Just out of curiosity, can I ask where you got her and what breed she is?