It sounds like there is a part of you that's not fully letting go of weaning too (which I can completely empathize with). You have to be fully committed to it to make it happen. If you're not, your daughter will sense that and take advantage of it.
I weaned both of my boys around 21/22 months old, mostly because I was ready, but I also felt that they were ready too, just needed to have that last thin string cut. I knew I was going to miss the connection time, but I needed to feel the freedom and wanted to increase their connection time with their father, which I felt nursing was hindering.
As for tips on what to do, I started by explaining about a week in advance that the "Bo-Bo" (the name they both picked for my breasts) were turning off soon, then I set a date a week later, lovingly (but firmly) communicated the daily countdown at nursing time, and stuck to it. I set the date to be a weekend so dad could help out too. If they asked to nurse, I would just explain that the "Bo-Bo's" are off and have no more milk, and offer them something else to drink or a few minutes of cuddle time. We moved the cuddle time with my husband as much as possible too, to start building that part of their relationship more. The "off/no more milk" was a simple thing for them to understand to help them realize that it's all done. There will be some whining, but if you stick to your guns and show her that you're serious, she will accept it. It took my first one a few days to get beyond it, and my second about a week.
Obviously your going back to work has made her want to pull you in tighter the strongest way she knows how, which is nursing, so in addition to staying firm with the "off/no more milk" idea, show her other ways that you can connect. Maybe just cuddle with her at 4am, and/or pick a special song to sing to her or something along those lines.
I don't know if these tactics will work for you, but I figured I would share my thoughts anyway. Best of luck to you!!