There's two ways to look at that.
1. More work and stress for the MC. Offwork work is the worst. I hate her for doing that.
2. SHe likes the MC and is trying to get closer to him by pretending an unreal lack of ability to draw and using job as an excuse. The worst way possible, but still a way. And I still don't like her for that.
In both, that's the worst way to do things. Please, the MC must say no. There's a limit for everything. If he teaching her had no relation with the job, it'd be cute a cool, but job related things outside of work hours is disrespectful and stressing.