Let's call the number of hours the waitress works in the evening "x".
According to the problem, she works 1.75 hours less in the afternoon than in the evening. So we can write an equation using this information:
x - 1.75 = 5.125
Now we can solve for x:
x = 5.125 + 1.75
x = 6.875
Therefore, the waitress works 6.875 hours in the evening.