I don't know if it's intentional but it seems like a lot of people here are talking as if there were "rules", like "x% is fair, y% is unreasonable". There are rules of thumb. But compensation is a marketplace. If the founder has no leverage, taking a lower stake in exchange for salary isn't honorable. It's just stupid.
Both parties need to feel like they're getting a square deal. If either of them don't, it doesn't work.
* Maybe you really did do a majority stake's worth of work, and she was just inexperienced.
* Maybe you didn't really do a majority stake's worth of work, and she felt like she had gotten shafted. You did start her at 6%.
* Maybe she was just a bad employee and a crap dev and wanted the paycheck. You weren't experienced enough to notice and fire her.
* Maybe through no fault of her own the project became untenable (for instance, maybe the spec changed a bunch of times, or you couldn't hammer out a reasonable set of features to launch on --- this has happened to us lots). You ran out of money, and she couldn't stay, good faith or not.
What are you going to do different next time?
If I was hired to do a project, and my payment was inline with my market value, I wouldn't care what my employer is doing as long as I kept getting my money.
$6900/m sounds like market value to me. If I was in the nurses position, I would have offered 1% equity on top of $6900/m
Of course, there are two sides to every story.
If you make a mistake when you negotiate a position, you are not ethically required to "ride it out" to some foreordained date.
Like I said, it's one thing to negotiate better compensation, or to walk away for a better offer, etc. It's another to say "I can screw you over and I will use that to get more from you".
And like I also said, there are two sides to every story. This is seen exclusively from the owner's side.