Guess and check.
Jane won 14 game = +14
Jane give 11 chocolate = lost 11 game
Total Jane won =14-11=3
But she didn’t...
so Mary won 14 games, mean Jane lost another 14 , she have have to give Mary -14 chocolates
At last Jane 3-14 = -11

Total game Jane
win = 14
Lost = 25
Total = 39 games

Another assumption method
Assume Jane lost all games as at last she have to to give 11 chocolate in total.

Therefore,
If lost one =-1 chocolate
If win one = +1 +1 =+2 chocolates ( mean 1 from Mary and 1 from she lost)

Given
Lost -11 = 11 games
Win 14 = 14 x 2 = 28 games
Total game =39 games

For every game one person wins, the other person has to win one as well to win back that chocolate that he/she lost. (You can consider this as drawing level)

Since she had to give 11 chocolates in the end, this means overall she lost 11 games more than Mary.

The 14 games that she won were drawn level by the Mary winning 14 games. Then
She lost another 11 games to Mary.

So 14 x 2 = 28
28 + 11 = 39