This is something i realised not long ago. In the movies and TCW animated series Aayla has 1 blue lightsaber In SW Battlefront 2 however she has 2 lightsabers. In the PC version she has a blue and green one and on the psp version she has a purple and green one.
she also has a purple one (seen in the psp version of BFII), i really don't get it. Maybe it's just a screw up from the creators...
I think you answered your own question with the first post. She has one in the movies and TCW and two in a video game, perhaps in the comics as well but I don't know about those. Within the canon hierarchy I believe this inconsistency falls into the realm of gameplay, which makes it non-canon. However, if you prefer her to weild two sabers just say that she has two but only feels like carrying one most of the time, or that Grievous took one of them as SBD said.
In BF2 she had purple and blue in the cutscenes, But green and blue in the gameplay. Obviously just a screw up.