How far are you comfortable traveling?

During your third trimester, how far from your doctor are you comfortable traveling? 
I'm 30 weeks now and my SIL just told me she wants to plan a shower for me but it would be a 5 hour drive away. Am I crazy for wanting to say no? I feel like it's too last minute/ and I'm too busy, plus I really don't want to go that far away. Maybe if it was this weekend haha but it seems too late to just now start planning. Am I being rude if I say no thanks?