Answer:
12 times
Explanation:
This is a unit conversion problem. In order to solve it we need the equivalence between this two measurement units. Which is:

This equivalence can be used as a conversion factor like this:

Applying it to the problem we can convert from gallons to quarts:

Now we know that we have to fill up 24 gallons of water and as we will do it with a 2 quarts pitcher we will dive it by 2 to know how many times we need to fill up this pitcher:

She needs to fill the 2 quart pitcher 12 times to make 6 gallons