A 75 Amp hour battery is a group 24, and an Optima is a horrible choice for a deep cycle battery. It is not enough battery for her current level of amperage consumption... 37 amps in 24 hours, and that battery is being worked to death with a 50% or greater level of discharge. Great way to destroy a deep cycle battery.
A 2012 dated battery, by Optima, is about done by now... she really needs to complete an equalization charge on that battery to 16.0V pronto, like in yesterday, to see if it is salvageable.
Do a search on how to equalize charge a battery here by mexico wanderer
What she needs is a good 30 amp charger that will output 14.8V at the battery, and a run cycle of a minimum of 2 hours, first thing in the morning, on the generator.
I'd suggest 2 things... a real industrial grade deep cycle battery like a pair of 6 volt GC-2's from Costco, wired in series, for 210 amp hours, or find a good used Teleco 140 to 150 amp hour 12V AGM type battery for sale on Craigslist, and charge it at 13.6V.
The charge controller she probably has now in her Casitas, is for RV parks and pedestal full time hook ups, not for dry camping and boondocking, which it is inadequate for.
She needs to run the fans and water pump only when absolutely necessary, and I see a 160W folding portable solar panel in her future, if she want's to keep the generator turned off and quiet.