She also has raised scales
This could be a sign of dropsy along with the bloated belly. I am not the betta expert by no means, but these two characteristics are symtoms of dropsy. I believe it is easily treated, however I would suggest that you be very careful with any medicines you place into the tank. Most times it is better to filter the tank with the meds in it (but with any activated charcoal filter media removed as this will soak up meds quickly). Most any fungal/bacterial product will work but please learn from my own mistakes and read directions carefully. Most times you must do a water change between doses or risk an overdosing situation. IMO, meds are sometimes a high risk endevor and can be worse that the disease/sickness they are meant to treat if used improperly.
I agree that even labrynth fish gasping for air is a bad sign. Do you have an airstone in the tank or does your filter return flow create surface disruption (sorry, that is a bad way to explain that, cant think of the exact term right now). Anyways, it is important to note that the bubbles from an airstone are not the main source of dissolved oxygen in your tank but it is actually the disruption of the surface water when the bubbles hit the top of the tank that promotes the best gas exchange in the water (meaning CO2 out of the water, O2 in). A filter's return water flow can also do the same and it may help to keep airstones out from underneath the filter return to create more surface disrutption over other areas of the tank.
Lastly, do you keep a male betta fish in the tank with your female(s) on a permanant or regular basis? I do not know if a female betta fish will generate eggs if a male is present or not, so that is why I ask. If so, some of the problem could be from stress to the female by the males and the two should only be placed in the same tank for an hour or two for breeding and then seperated again. I did not know this and just learned about it and thought that was interesting and noteworthy for you possibly.
Hope this helps a bit.