Sounds like you are on the right track, and pp is right... if she is Angel then this probably won't be too hard to fix. I recently had to completely change how I put Nathan down to sleep, because he started putting up such a fuss. He was struggling and fighting me as I held him to rock and sing before putting him in the crib, as we have always done. So in the last few days I have just zipped him into his sleep bag (an armless sleeping bag thing that makes it hard to go on all fours or stand up) and given him the soother and his lovey, and before I leave the room he has put himself to sleep or is well on his way. Maybe she is ready for a bit of a change, too? We also top off with a bottle before bed, but DH does it out in the living room sitting up so DS can't go to sleep yet. It does sound like she is addicted to your help going back to sleep at night... if she is only BFing a few sips, then it is not hunger. If DH could start getting up with her for a while, then that could break the association.
You could try to extend that last A time just to see what happens... what's she gunna do, wake up at night? She's already doing that, so there is no harm in trying.
I think you are doing a great job trying to get her to settle on her own; it can be so hard, so stick with it! Teaching her to sleep better is a gift for your whole family, because you will have more energy for DD1 and DH as well as DD2. It has been a few months, so it will take some time before new habits are formed. You just got back from holiday, so it is a great time to make a fresh start... she is already trying to adjust to being home again, so she might as well adjust to some new things, as well!