No, you can't sort a ditionary.
Looping through the keys in the dicionary, allows you to get to the value which is the count of the letter. You should be able to use our basic idea of finding a max, saving the letter along with the updated value of the max.
What if you find a second value which has the same max for its count? Then check if that letter is earlier in the alphabet. Letters are really numbers "under the hood" and therefore can be compared using < and >.
Another strategy that is less efficient loops through the dictionary more than once.