What should I do?

Sorry it’s a long post but please give me some advice. Baby shower is supposed to be December 15th. My cousin is planning it. I gave her a list of everyone to invite names and addresses. She wants me to help send out invites cause it’s a lot of addresses to hand wrote. I agreed but the last two weekends when I went to help her at my grandmothers she bailed and this past weekend said I should just do it cause I know everyone’s stuff. Then to make it worse it’s supposed to be at my grandmothers house. It will be very cold outside and fitting around 30 people in her house will not work so I suggested renting a place and she just gave me attitude. Should I just trust that she will get it done or just start planning it myself. It’s getting close to the date and it’s close to holidays. I’m scared no one will show up cause it’s such late notice now.