Kaua'i

My partner and I are both turning 50 this year, and while I don't care about celebrating my bday, my partner wants us to take a trip to Kaua'i. We would go the week of Xmas because we are both teachers and have that week off, and her bday is Dec. 23. Our main interests are being in nature and hiking (not hardcore hiking...more like 4-5 miles of meandering and exploring), and my partner likes the beach. From everything I'm reading, December is not the ideal time to go to Kauai because of how rainy it is (I know the south shore is typically drier, but if we're going all the way there, we'd want to explore as much as we can). Anyway, is it dumb to take a trip in December? The lowest estimates I'm finding for the both of us are around $4500-5000 for the flight from Los Angeles, hotel, and car); I wouldn't want to spend all of that $$ to be stuck in a hotel all week due to rain. Does my partner need to abandon her idea of Kaua'i in December, or do we just suck it up and do outdoors stuff in the rain?