In a week(5 days) she completes = 50 miles
In a week ,at treadmill she runs 5x 2.5 miles= 12.5 miles
Then she spends in elliptical machine 50 - 12.5= 37.5 miles in a week
So then
in a day she spends 37.5/5 = 7.5 miles
ANSWER is 7.5 miles in elliptical machine,by day