Let's say Gisele has x quarters. Then she has (x + 16) nickels.
We can express her total in change as:
0.25x + 0.05(x + 16) = 5.90
25x + 5(x + 16) = 590
25x + 5x + 80 = 590
30x + 80 = 590
30x = 510
x = 17
Gisele has 17 quarters and 17 + 16 = 33 nickels