Assuming the revenue is pretty stable (and not declining), I'd offer her 2x her share of annual revenue, or $20k. If the growth on the app is increasing rapidl

Assuming the revenue is pretty stable (and not declining), I'd offer her 2x her share of annual revenue, or $20k. If the growth on the app is increasing rapidly, you may have to offer more. These things are more art than science, but if both of you agree to a number, then that's the fair price.