im glad you are so in tune with your child's needs!
chances are you can reduce the amount of time she needs to be up by keeping lights low, not talking to her while doing the feeding, and even laying down with her; even if its the floor in your room. keeping her in the same room as you is a good idea; babies just like to have their mamas near, and having her in your room might help with that. :) our son was in our room (his crib was there too) until he was nearly 3, and he still comes into our room half way through the night. but ill remind you that he sleeps like a dream and has never had issues going to bed or going to sleep. :) thats the positive side.
she just sounds kinda like my son; will not accept substitutes for the real thing. its exhausing, but you will get through this. go to bed an hour earlier if you have to. take a nap when your kids nap (hopefully the older one will nap for you?) just do the best you can. the answer is likely already within you, you just have to trust that you truly DO have the specific instincts for your children. ;) just follow your heart. this distraction will only last a little while in the grand scheme of things. :)