30 minutes is 30/60=<<30/60=0.5>>0.5 hours.
Two 30-minute rest stops take 0.5*2-1 hour.
If she takes two rest stops per each half of the journey, then she takes 2*1=<<2*1=2>>2 hours in rest time.
With a load, at her top speed, she can travel 143 miles in 143/11=<<143/11=13>>13 hours.
Without a load, at her top speed, she can travel 143 miles in 143/13=<<143/13=11>>11 hours.
Thus, the round trip will take 13+11+2=<<13+11+2=26>>26 hours.
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