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It's going to be difficult and longer because she is used to going outside and most dog that have been taught to do that consider their home their den. It does become confusing to them if you then want them to go indoors and they may have accidents in other parts of the home. If you are determined to dog this then I would set it up outside on the lawn first and teach her to use it there to get her odor on it, then move it to the deck and place it inside an over sized crate or put an x pen around it so she gets used to her potty being surrounded by something, then you can move it into the house but I would keep the crate, or x pen around it for a while until she gets used to going in that spot.
Use a potty command each time you take her out on leash to use it and continue using that command even as she is eliminating, then praise and reward her immediately when she is done. Reward her with something that will really motivate her such as human food like chicken and this is the only time she gets this reward so she associates it with going on that spot.
The potty patch may also have some training tips in it.
Personally I would take a shovel and shovel out a potty area outside for her as you may be opening Pandora's box.