A single dwarf gourami in a 10 gallon should be just fine. You're doing everything just right for her. It's very obvious how special she is to you and that you're giving good care.
Sorry I misunderstood about the filter changes.

In the meantime, unless there's some unknown source of source of nitrates such as decomposed food or dead plants matter or if you haven't vac'd the bottom for a while. after you do a few 50% W/C you should be fine with one 50% change a week.
Good luck with her.