wtf is wrong with my fish!?

Housing
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?

Food
What type of food do you feed your betta fish?
How often do you feed your betta fish?

Maintenance
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia:
Nitrite:
Nitrate:
pH:
Hardness:
Alkalinity:

Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?

20g with nothing other than the fish and live plants. 6 fish, all have been fine througout, infact only this one fish has ever had problems.....besides i had one WHO JUMPED OUT TWICE in the same day!!!!! which was a big drop, i treated her and is fine now. took a video cuz i thought id lost her it was so bad..
Back to the fish im worried about; she has been the only fish to ever show health problems, although swimbladder is really the only thing, none others have had any symptoms. This fish never shows signs of distress, no color changes or stress stripes on her body. I have one who stresses out real easily tho, a delicate one, and even she has never had anything wrong with her. This fish also never has any appetite problems, and seems to be nearly as active as the others. When i previously mentioned she seemed lethargic, i was kind of wrong. If anything, she just seems slower, yet is just as active as the others. This fish can quickly move when need be, but not as darty(?)sudden fast movements) as the rest, prefering a slow pace........................................

And wow, looking behind me now, 20 minutes later, it seems to have passed. all in a day... She was laying completely on her side floating, just those 20 minutes ago. Now has her buoyancy back...wow. wtf is wrong with her. I wont feed her today.

Back to the question; My tank all seems to be in balance, all in good health according to my research. i test it often, since i have noticed this problem. and ive never had any fluctuations in anything. my only problem lately has been algea. since i converted over to this fluorescent strip light, and 20g. I use no chemicals besides my bimonthly fertilizer liquid, and ive had to cut way down because of the algae.
I dont believe it is my tank since ive changed it out quite a few times, with new everything.
I never like to say this, but i got a filter from my family, who has oscars. I thought the biofilter was new or clean, since it had been cleaned and unused for a while. well, i got ich from it, which was treated hastily, and has yet to return. I was very worried that is when(if) a parasite took hold of my ginger cambodian betta booty! but, that was a long time ago, and there has never been a decline in physical health, nor have any other fished showed the same symptoms.
wow i didnt mean to write that much, ill shutup

I have been busy, but wanted to mention this all earlier:

The last few days her swim bladder disorder has only gotten worse.

I have fed her only 1 pellet(soaked,soft,her normal diet) on 2 separate, consecutive days. The 2nd feeding had givin her problems again, and just as serious as the last(my first post).

ATM she has a touch of it, but retains much of her buoyancy, able to swim effectively, but still quite impaired.

Her overall health hasnt degraded any, excluding the sudden-sharp incline in swimBDO. She always appears with perfect behavioral and physical features. NEVER showing any sign of distress. ALBEIT, I often see her sad lil flat face gasping and recycling air, trying to relieve herself....
AND SPEAKING OF; I saw her pass gas, and quite a bit, 4-6 little bubbles yesterday.... I hadnt even treated her with anything.

PARTICULARLY INTERESTING INFO I HAD FORGOTTEN TO LAY OUT:
A looong time ago. Far, far...anyways, around the time i first obtained this fish, she had gotten into a VERY gnarly fight, where a good chunk of her belly(where the "egg spot" resides) was torn asunder, literally. although it was only a few small pieces split, it was a pretty gruesome wound.
I remember the area was a bit shredded for a short while, and even tho the wound itself wasnt very(if any) bloody, her bowl movements were, for a good few months, and I was very worried. It passed and she passes normal now, I am not sure of how often tho... which actually may be a worthwhile study...
Honestly, i had kinda forgotten, I have not examined the area in some time... i will do so tomorrow.
This could be significant, but there cant be any chance of an infection after so long, right?
I cant understand why she is so susceptible all of a sudden. Not that she was nearly immune, being infected with the disorder on maybe 3 other separate occasions, all dating months back.