Re-evaluate the business relationship - she's not really a 'co-founder' any more, or perhaps never was. Revisit the relationship and make her employee #1 with a moderate equity stake, or just an 'advisor' who's given some equity stake in the project. I'm assuming you're 50/50 on this (which I'm not sure I could ever bring myself to do personally) but she's certainly not contributing anywhere near 50% of the initial work, and apparently she realizes it.

Keep the friendship, rework the business relationship to something fairer to all involved.