Two dives a day (45-60 min/dive?) really isn't logging that much bottom time.
Is your girlfriend making sure that she stays well-hydrated before and after dives?
Does she have any allergies or mild asthma?
Is she taking antiseasickness meds for which dry mouth/throat is a well-known side effect? It's very common for antihistamines, e.g. Dramamine, scopolamine, to have this side effect due to anticholinergic activity. FYI, users dosing with Bonine (meclizine) tend not to complain of the dry mouth side effect as often.

(Fortunately, since Bonaire features a lot of shore diving, she probably won't need to take such meds!)
Metal second stage regulators generally help with the dry mouth phenomenon. The moisture in exhaled air condenses on the inside of the reg and humidifies inhaled air somewhat.
For dry
mouth, I've heard of some people swishing some saltwater around in their mouths during a dive and then spitting it out. This technique probably wouldn't help with dry throat, though.
Scuba gas is dry; there's no getting around it. I've personally never used the Apollo Bio-Filter, but honestly I wouldn't worry too much about the addition of failure points.