Oh I am so sorry, that sounds so stressful. A couple of thoughts, although I am sure you have heard just about everything having seen so many doctors (what are they telling you??) Does your daughter like baby dolls? Can you start to have her put her baby dolls "night night" and tell them how important it is to sleep, etc. Have her sing to them, hug them, etc. My DD is also 2 and really responds well to ROUTINE, we do almost the exact same thing for bedtime, wind down, etc. every night. One of the other things that seems to help settle her is reading books, as she gets older now and more interested, this is taking longer and we have to read quite a few books some nights. There are lots of great bedtime books to keep the conversation, focus on the goal: SLEEP!!!
Because you also have a baby, it is definitely normal to see some jealousy, neediness, etc. Is your DD needing more 1:1 attention? My son is now 8 months and he also barely naps at all, but has started going to bed by 6:30 p.m. The great thing about this is that it allows my husband and I to give my daughter undivided attention for an hour or so before bedtime, she seems to really need this.
Also, definitely try and get her outside whenever possible. At 2 years old, they need a LOT of phyisical activity. This has been such a long winter, I have definitely noticed a difference when I am able to go outside, even if it is only 20 minutes. So, elicit some help from others for the baby if you can take your DD on some walks!!
I hope you get lots of good advice and wish you luck, keep us posted on your progress.