Should I pay for my fiancee's parents' trip?

I'm currently debating with myself right now if I should offer to pay for my fiancee's parents' trip or not. They're flying in to meet my parents and will be staying until our wedding day. My girlfriend and I met through an international brides dating agency. Probably not the most romantic for some but it was actually pretty sweet for both of us. Two years after meeting each other, here we are now, living together and counting the days until we tie the knot. In our 2 years, I've only met her parents twice. That being said, I need to know if it's my obligation to pay for her parents' trip from Mexico. Even if it's not, should I still do it?