Having had a fancy goldfish in the past who was very prone to swimbladder problems, battling to swim without floating up like a helium balloon or spending long periods of time floating upside down, I've tried and tested various options. Usually, the "line of treatment" went as follows: (i) dietary - feeding more peas or bloodworm and much less dried food; (ii) aquarium salt treatment [NB may not be suitable for tiger barbs]; (iii) medication - swimbladder or internal bacteria infection treatment.
Have you noticed whether her swimming action improves after pea/bloodworm rather than after dried food? You could try reducing the dried food for a week or so and increasing the pea/bloodworm food during that time to see whether that makes a difference. I've also read that spirulina can work well for swimbladder problems.
As she's still behaving normally otherwise, and especially after 2mths of this, I agree with you that best not to move her - the stress may do more harm than good. If she deteriorates, then it might be worth moving her and increasing the non-dried food in the QT to see if that makes a difference. As for aquarium salt, this often worked wonders with an overnight improvement for my goldfish BUT many tropical fish don't seem to tolerate salt; however, it seems that some do tolerate "salt dips" ie rather than the tank being treated with salt - maybe someone else can advise on this? Finally, if dietary or salt treatments didn't work, then I used a medication which often solved the problem, at least temporarily; my own experience with using medication with tropical fish, and reading of others' experiences (eg Sue's), is that tropical fish are less tolerant of them and so I'd definitely leave that as a "last resort" option.
Hope that helps.