Gosh! Bosses...and if I understand in this case...business owners are people too!

If you know you are going to be leaving why not give all the notice you can? She knows you hve been going to school and I am sure expects some change upon your graduation.

You may find you want to keep a "hand in" and teach piano occasionally or as a supplement. How much better if you have left on the best possible terms.

You could start giving "warnings" and ask what you can do to help her find replacement. Between now and August you should be able to help her work it out.

Yes, two weeks is standard in the corporate world, but isn't this a bit different? What would you want if you were in her position?