Sometimes, you just have to do these things. It's not about you; no one is going to be concerned with how you're acting or judge you for not sobbing and sharing stories. This time isn't about you, so they're not going to be placing you and your demeanor as top priority to scrutinize and pontificate upon. You go because you're an adult, and you're representing those who would be there but cannot due to circumstance and location. Yeah, so you didn't know her that well, I get that. But honestly, if that's your reason for being awkward, then you have a lot to learn. You're gonna be in worse situations, ones that will make this one look like fucking paddy cake; I suggest get over the awkwardness and go. Put on your big girl panties, go show up for your family with a brave face (a simple "my family's condolences are with you" will suffice) and then get on with your life; at least you get to move on with little to no sadness.