Definitely not 2, but I think you can get by with one. I use Instant Ocean and keep mine on the heavier brackish side, and have about 12x filtration going at all times (3 separate filters - 2 on the back, 1 canister). In one level of the canister, I took out the bio-balls and filled it with ammo-chips to further reduce ammonia/nitrates. She's been doing great with this set up, always ate well until I changed out the substrate. Took it out, and she's back to her normal self again.
Also, I realized another reason why she may have stopped eating and lost weight. About a day or two before I changed the substrate, I started buying a different kind of shrimp that was smaller and already peeled and tail removed (raw, frozen). I don't think she liked them, which is why she didn't eat them, and I also think they had less nutrition than the larger shell-on ones that I had been using previously (I de-shell them because she doesn't ever eat it anyway). I bought more of the regular ones today and she gulped them down in a heartbeat. Turned her nose up at crab meat and salmon though. :/ If you get a sabina, I'll keep my fingers crossed that yours is less picky than mine when it comes to food.