Hanneli,
Just wanted to offer some HUGS!
We've been through some serious OT bouts and with my lo's and with them, there is no getting back on track until they have caught up on sleep- at least a little bit!
I HATE extending naps and maybe if that's not working for your lo, you could keep working at extending one nap and trying something else to extend the other - just until she's caught up on sleep. Maybe snoozing in the car or stroller?
I would definitely keep the catnap until she's caught up and then work on cutting it. My guess is that she's ready to drop it, but right now it sounds like she needs all the sleep she can get! But for your sanity, make it a swing/stroller/car/whatever else works nap