My 3 yo JUST got off a bottle! It has been very hard. We almost had her off it a year ago by simply cutting down on it. She was allowed one only at bed/nap time (which meant saying - no, bottles are for sleep time)and we diluted it with water which helped make it less appealing. She spent a week with my in-laws which destroyed our months of weaning and then I was pregnant and terribly sick and I just couldn't pick that battle. We finally tackled it again when I started to feel better in my 3rd trimester and let me tell you what we realized - Weaning is not for a time when new siblings are joining the family. If you don't breastfeed (we did both with the 3yo) you might be able to try "you're the big girl, let's give the bottle to the baby", but if that doesn't work - give her a little time to acclimate before pushing her to get rid of her "comfort". My son is just 10 weeks (exclusively breastfeed)and we are two weeks without a bottle now. But she definitely needed that time before we pushed for such a major change.
(We just told her we were out of bottle liners and she can have a drink next to her bed like mommy)(she did ask for a few days and I would say - "oh, ya. Could you remind me to buy some at the store, b/c we keep forgetting)Now she's over it.
\It was weird to see my 3 yo with a bottle - such a big girl, but in every other way she is developmentally WAY ahead of the mark. Big vocab/talker, recognition of letters and #'s and so on. No horrible affects of being a 3 yo bottle drinker.
so, give your girl a break until she's settled into being a big sister.
Best of luck and congratulations.