Although I had never heard this expression in the sense given to it by Aaron Israel Lion's Franc, it is consistent with the idea of "putting on your pants" as "stopping resting and preparing to do a task." Still, I think it's a mistake or a trolled for tightening her belt.
In Colombia the expression "fastening your belt" means saving, incurring only the expenses that are extremely necessary. Enter a period of austerity. Sobriety, abstinence, moderation.
Fastening your belt in the Yucatecan colloquium means being prepared to face a problem. Literally it would be to fasten your trouser belt. Some synonyms, words or similar expressions may be prepared, decided