As happened here, apparently.
There's a whole chapter on this problem in most introductory game theory textbooks. The basic problem is that you cannot directly control how hard someone works, you can only give them incentives to work hard and then measure the output. Much as you'd like to say "She's a professional, you're paying her, she ought to do a good job," the real world doesn't work that way. She'll do a good job if it's worth her while to do a good job.
The economy is not fair. You can try to pretend it is and watch all your ventures get driven into the ground, or assume that you're going to get a raw deal sometimes and only take those raw deals when it leads to a sweeter deal later on.
I paid the 35% equity 8 months ago, only to have her quit when the going got tough.
My comments are mostly intended for bystander-readers who're thinking of doing the same thing - paying a technical developer a full salary + 1-5% equity to develop a product from scratch. There're a lot of people that still suggest that, and it really doesn't work, as you've found out the hard way.
I dunno what advice I'd give to you personally - it's a hard situation, as many others have pointed out. Probably cut your losses, chalk it up to an expensive learning experience, and move on, then try again some other time. As I mentioned in another comment, I think it's fairly unlikely that this developer left you usable code that someone else could pick up, so it'd be difficult to get a contract developer to push it to finish line. You could learn to hack yourself - Python and Django are not difficult - but it'd set you back at least a couple months, and then you'd still have to implement everything.
[Edit: last paragraph was on the assumption that her work was not even demoable, but rereading your post, it sounds like you've gotten to alpha but just need to incorporate the feedback in. If that's the case, a contractor might work, but be aware that it's harder to read code than to write code, and if the code quality is bad enough any contractor would just have to throw everything out and start from scratch.]
If you can find a technical cofounder, someone that you trust that you know is a good developer, I'd do that (and give the decent equity from the start!), and then they can probably write the whole site from scratch in a couple months. But it has to be someone you know well, someone whose skills you're sure about, because otherwise you run the same risk with them.
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.
Unless you were paying the developer very little, or nothing, that is when equity should be used as payment
35% is a LOT with $6900/m