Probably a weekly 100% water change is necessary. It also gives you a chance to wash her gravel and decorations to clear off any organic matter than might have settled on them. A 50% water change or two in between full changes definitely wouldn't hurt either.
If you're worried about using too much of the detox chemical, maybe getting an empty gallon milk jug or two (cleaned thoroughly first) and pre-mixing changing water might help. That way the water isn't over-treated and the balance in the tank is maintained when you add it.
Having never used a gravel vacuum I can't give you any suggestions there. Sorry! Maybe using it when you do 50% changes to help keep the tank cleaner between full changes?
Testing your old tank water is a good idea if your fish seems under the weather or right before you change the water, just to see how long it takes for certain levels of ammonia, nitrates, and nitrites to build up. It should give you an idea of when you need to do full or even partial changes.
Sorry for the novel. Hope this helps!