(((hugs))) It's so hard when there is a new lo and everything goes to pot with the old one - particularly when things have been going so well before.
Firstly, I suspect that you might be battling some OT issues. Not so much that her sleep needs have changed, but that she has been ill and stressed and battling with you for a couple of weeks and needs a bit to catch up. My first move would be to try putting her down for her nap about 15 mins earlier than usual - not a huge amount, but hopefully enough to catch her before she goes over the edge, iyswim. And I would also bring bedtime earlier on any day when her nap isn't as long as you believe she needs it to be.
I have often found that behavioural things that seem unrelated to sleep get a lot better when OT is taken out of the equation.
Secondly, I would give her as much reassurance and as many cuddles as you can possibly manage. I remember how hard it was to carve out time for number 1 when number 2 came along, so you have to be really aware of how much time number 1 is getting. If you can, I would aim to read her stories whenever you are feeding, so that she sees feeding time as a time when you can sit down and snuggle with her and pay her attention. If your ds is sleeping, you should try to do something that she likes with her, and if you can you should try to create a bedtime routine that has a part which is not to be disturbed for any reason - with my 2, I used to feed dd2 after bath while I sang some songs with dd1, then take dd1 downstairs to watch some tv while I put dd2 down. Then after the programmes were finished, I would take dd1 up to her room and read her a story - and even if dd2 cried during that time (maximum of 10 minutes), I wouldn't go to her as I felt it was important for dd1 to know that sometimes she was my top priority.
Thirdly, I would make a plan for the messing around at bedtime and stick to it (and go through it with dh beforehand and get him to agree to it as well if he is going to be involved in bedtime). For us, when we had the endless calling back, we addressed all the likely requests before the light went out (last cuddle, last drink of water, check that she had every toy she wanted etc) and then after that every time we had to go back we were firm that she had everything she needed and it was sleepy time. I suspect that you will find she adapts to it more quickly if you don't give her a kiss - I got caught in the "cuddle trap" where clearly dd1 was getting something out of me coming back so it was worth it for her to call me. After the night where I was called back 15 times for "one last cuddle", I stopped going past the door to tell her it was time to sleep.
And lastly, I really doubt that dropping the nap would help - and I am fairly sure it would make things much worse. Stick to your mummy instinct - it's normally right.
