Oh boy, I feel for you!
I know it must be hard with a little one in tow, but if you really want to get her out of diapers, you just have to stick it out for two or three weeks, ditch the pull ups and clean up after her. It will be exhausting, no question, but pull ups really DO NOT WORK. They are a marketing trick simply invented to get you to spend more money on diapers.
The one thing you have to commit to is not showing your frustration. If you get upset about cleaning up after her when she has accidents, she will have a negative association with toileting and it will make everything ever so much harder. Praise or even reward potty success and simply deal with accidents without much ado.
Prepare her for the next try. Set a date, consider a long weekend or a period when your husband can help with the baby (vacation maybe?). Talk about how she is a big girl and you won't be buying any more pull ups... and then do it. Use up all your pull ups (or hide any leftovers) and be done with them. Expect lots of accidents for a few days, but if you stick to it and keep your calm, it will let up! Take extra clothes with you wherever you go... just be prepared.
Also don't delay nighttime training. I found "puppy pads" so helpful. I double or triple layered my daughters bed with sheets and puppy pads, so I could just rip off a layer in the middle of the night when she had an accident.
Almost all children go through an initial period of success and then a short bout of regressing with many accidents. If you just stick it out you will be successful in the end.
Good luck!