My opinion too.
Playing with herself was disobedient but she might have got carried away. Lying was a calculated offence.
When my ex-slave made that mistake I felt that humiliation was a more effective punishment than pain (well, it's hard to punish a pain-slut). I wrote I LIED TO MASTER on a freezer-clip and put it on the end of her tongue; it didn't hurt a lot (I checked), but she had to go round with her tongue stuck out showing off the message on the clip. I told her she would wear it for the rest of the day, but inside half an hour she was weeping for mercy and promising (indistinctly) to be good as gold forever.
And from then on she knew that the "Lie Clip" was in my toybox waiting.