How many games to play in a chess match? I gave someone 3 months to become as good a chess player as I am. She was just a beginner and I'm a slightly below average player (around 1500 elo).

To see if she managed to do this, I figured we should play a chess match consisting of multiple games. 

But what is a reasonable or standard amount of games to play in a chess match (or a 2 player tournament, if you will)?
The amount of games in a match is usually* even, to guarantee an equal balance between White and Black. 2 game (mini)-matches are rare, except in knock-out tournaments like the Chess World Cup. More games will produce a more reliable result, so you should play as many games as you have time for, but 4 games should already give a good indication about who's the better player. With some mathematics and the expected performance formula you can calculate the odds of losing an X-game match to a player who is Y ELO points better/worse than you.

*: The only exception is an Armageddon game which can be used after a match which ended in a draw (i.e. the same score for both players).