I usually have difficulty keeping cool no matter where I go. The key for riding in the tropics for me has been soaking clothes in water, then trying to keep moving. Special vests and neck scarves which are designed to cool you off have been helpful. Having a system for rapidly shedding riding layers when necessary--at borders, for example, or in city traffic--can be key. For me, that means easily-accessible cable locks for loose items like jackets and helmets.

I'd be wary of any statements about how hot it will be heading south this time of year, especially if they're attached to recommendations you wait to purchase cold-weather gear. It's easy to hit elevations of 10,000 feet/3000 meters or so in Mexico, and almost inescapable to ride briefly over 11,000 feet in Costa Rica. Add some fog, afternoon thunderstorms, or seasonal rain (the rainy season is NOT going to be over in a month or two), and it's easy to get chilled.

FWIW, I don't use mesh on this sort of trip. Seems to work for some, but not for me--too many days which range quickly from hot to cold and back again. This includes those sudden, unexpected downpours which can quickly chill to the bone if you get wet.

If what you were asking was specifically about clothing for women, best ask again more succinctly, since you've already attracted the answers from the usual coterie of bickering men (including myself).

Hope that's helpful.

Mark