Even though she's litter trained now, she may feel the need to mark her new territory when she moves to a new location. I'd suggest starting slowly. Keep her confined to her cage for the first week to help her feel secure and safe in the new place while she gets used to the new sights, sounds & smells of that new home. (We always did this when moving to a new place with our rabbits.)
Then, when you let her out, keep it confined to the area immediately around her housing. Don't allow her the whole downstairs at once. Keep the area confined. Gradually, of course, she will work up to being able to roam the whole downstairs. Just don't give her too much space too soon. Doing that will help her during the transition and allows her to know -- for sure -- just where that litter box is. It also prevents potty accidents. What you definitely don't want is for her to accidentally potty where she shouldn't because they tend to go back to the same place again and again. Better to prevent accidents by going slowly.
If you do decide to add a second litter box, I would not do it until many weeks down the road and after she has had all that time to transition gradually to the larger area.