I don't see why you'd think a month before your due date is too late for travel, unless you're high risk or have a medical condition I can't imagine a doctor telling you not to travel, its not a foreign country...
It's very considerate of you to think of your friend, but if that's the only day that works for you, she'll understand and unless you and she have multiple friends and relatives who'd be invited to both events and would have to choose - it shouldn't matter.
You seem to be putting the cart before the horse though. Let someone offer to host a shower for you, then they'll figure out the logistics.