good luck! highway doesn't use the battery much, it's everything else. but you should be fine. how many miles on her?
Is there an elevation change of more than 100 ft in that entire trip? That won't be exercising the big battery much, unless maybe the OP gets into stop and go traffic from road work or a wreck or something like that.
Yes the risk of the Prius not making this trip is similar to the risk of a parachute not opening when you do sky diving. Go for it!
Watch the oil level. If its a burner it could run out of oil and ruin your day. High speeds can accelerate oil consumption.