Your idea provoked me to write a little script in tcl to count them in all the novels. My process:

I copied my downloads of the Gutenberg files of all six novels;
I deleted the Gutenberg legal and commentary information;
I edited out the html markups that conflicted with tcl commands ("<>);
and ran the script on all six files. I'm pretty confident it's accurate. Results:

Persuasion.txt:
persuasion = 4; persuade = 8; persuades = 0; persuaded = 12

Emma.txt:
persuasion = 4; persuade = 14; persuades = 0; persuaded = 26

Mansfield Park.txt:
persuasion = 2; persuade = 18; persuades = 0; persuaded = 18

Northanger Abbey.txt:
persuasion = 5; persuade = 8; persuades = 0; persuaded = 5

Pride and Prejudice.txt:
persuasion = 6; persuade = 17; persuades = 0; persuaded = 20

Sense and Sensibility.txt:
persuasion = 11; persuade = 8; persuades = 0; persuaded = 16

It's pretty clear that the theme prompted Austen's brother (Edward, was it?) to rename the novel, rather than the frequency of the words.