The Godmother of My Child

I have a cousin who's a year older than I am. (She's 21, and I'm 20.)
Although we are very different, She's the closest thing I have to a sister and it's always been a known since we were little that she'd be the godmother to my kids. Well I'm pregnant with my first, going to be 33 weeks on Monday. She hasn't been involved in my pregnancy or engaged in any of my pregnancy related events AT ALL. She didn't offer to help with my baby shower or anything. Instead, for my baby shower last weekend she barely said hi, just more of a shady wave, then got shit faced drunk and cried about her ex boyfriend. Which I asked everyone to be mindful of their Alcohol intake as this wasn't a drinking fiesta, but my baby shower! 
I'm not the one to get my feelings hurt, I tend to brush things off... But I can't get over how she acted and treated me for my baby shower but I'm supposed to let her be the godmother to my daughter. I did absolutely nothing to her... 
I don't want her to have such an important title in my daughters life if she can't act accordingly. If she doesn't know how to treat me, why would I want to have my baby around her?  
But I also don't want to hurt her feelings...  Which makes NO sense considering she hasn't cared about mine. 
What do I tell her?