How I’d do it: 
5/6 three times makes 15/6. Made into a mixed fraction is 2 3/6, which in its simplest form is 2 1/2. 
When converted to ounces, assuming that 6/6 is one complete ounce, then you get 2.5 ounces. 
The total weight she picked up is 2.5 ounces.