She is speeding
First you need to converted miles into km as she was driving with miles but our speed limit is km so to maintain the balance we have to convert the measurements into one unit 
Speed limit was 80km 
She was driving 75 miles
We know, 
1 mile = 1.609 km 
So 75 * 1.609 = 120.675 km 
So speeding = (120.675 - 80) 
= 40.675
Therefore, she was over 40 km speed limit