There are a few possibilities.
First, since you took her to the vet, let's rule out medical problems.
If she and the dog conflict, she may be marking the couch blankets as her territory. She needs to know that peeing outside her box is unacceptable. This can be done by grabbing her by the scruff of the neck (it's okay, mothers carry their kittens this way), bringing her to the "scene of the crime" and rubbing her nose in it while saying in a loud and firm voice "No, no, no!". Never, ever strike a cat. They will lose respect and trust in you.
When you let her go she will probably run like hell and hide. That's okay. She knows you're displeased with her and she knows why. Be indifferent to her for a day. Feed her and take care of her necessities, but deny her attention until the next day. Cats don't like to be "shut out" from their owner's affection, so this will help her remember.
The next thing you must do is treat the area where she peed so her scent is no longer there. If she smells her urine, the instinct is to go in the same spot. There are several enzyme cleaners on the market that do a pretty good job. Check with your vet for recommendations.
Another possibility is that she may be intimidated by your dog, and peeing on the couch is an involuntary, nervous act. Watch how she and your dog interact. Is she afraid of your dog, or do the appear to be comfortable together? Do they play? A cat on edge will often do things she wouldn't normally do.
In short, you must 1) let her know that going outside her box is unacceptable, and 2) find out why she's doing it.