We can find the diagonal distance using the Pythagorean Theorem (PT). PT is a formula that calculates the diagonal distance (c) when it knows the value of north/south (a) and east/west (b).
PT is a²+b²=c², so we simply need to substitute 3 and 4 in for a and b, respectively.
a²+b²=c²
3²+4²=c²
9+16=c²
25=c²

5=c
Using the math above, we can see the diagonal distance from her starting point is
5 miles.