Hmmm - those scales do look raised to me and there's definitely a sign that something is awry in the way she moves and hides.
At the very least, I would advise feeding a pea, with shell off and chopped into tiny morsels, just to eliminate the possibility of something internal such as an intestinal blockage compressing the swimbladder / buoyancy aid.
However, I think further treatment may be required - if feeding pea doesn't work, do you have a spare tank/tub, filter and heater that you could move her to? We'll advise further and whether / with what to treat once we hear how she's getting on.
Frozen pea ( not pee, though, as it's ammonia! ) is absolutely fine but it's easier to take the shell off if you pour a tiny bit of boiling water over it first to 'blanch' it - the shell should then slide off easily.
I would definitely focus on ensuring that ammonia and nitrite are 0, and nitrates no more than 20 above tap water levels - so do whatever frequency and amount of water changes are required to ensure that the water quality is consistently at that level.
That sounds fine for a hospital tank. Water in the hospital tank needs to ensure water quality is the same as described above, and the same temperature as in the main tank. Remove a small portion of media (sponge/foam) from the main tank's filter and put it in the hospital tank's filter, to ensure that the hospital tank is instantly cycled.
An Epsom salt bath might be a plan if the scales start to protrude any further. Alternatively, a bacterial infection treatment (e.g. Waterlife Myxazin or eSHa 2000) might get to the root of the problem if it's bacterial. However, I would concentrate for now on the pea treatment plus optimum water quality, then let us know how the situation is tomorrow.
I would advise doing whatever you can to get your nitrates as low as possible. Monitor them daily, and if the daily water changes need to be 50% to get nitrates down to 20 (or no more than 20 above your tap water levels), then do that.
Keep dried food to a minimum or avoid feeding it altogether, and only feed pea (which the fish may come to recognise as food) or else live/frozen bloodworm or daphnia, and hopefully this in combination with the water changes might help.
Good luck in locating her - squeezed in to some decor along its sides, in plants or seemingly inexplicably squeezed in behind the filter are all possibilities. When moving any of them, do so carefully for obvious reasons - and moving them cautiously may help avoid her darting and bolting to the other side of the tank in fright.