She is getting a little from school (both boys and girls talk like that, depends on what their home environment is like), the age 3 brings on an attitude because they are trying to be their own person as well as fitting in, but it also has to do with the new baby. Even if she adores the new baby addition she has been use to ALL the attention and now someone else is taking some of that attention.
Reinforcement: you and parents still love her, come up with how to best handle the tantrums that both parents and you can enforce so it is handled the same way each time, when she says something that you/parents do not like remind her that we do not talk like that or use those words and have "strict" bed time rules (we do not watch TV, you can get up to use potty but then right back to bed, and so on) will help. In the end it will just take time for her to adjust completely to the change, just keep reenforcing good behavior :)
For meltdowns we say 'We/I do not listen to crabbies. Please go to your room and come back when you are ready to talk without the crabbies.' At first it took 5-10 mins for her to calm herself down, now it takes less then a minute and she rejoins us. We also gave her the tool of when crabby to take deap breaths in and out, it helps relax/calm as well as something else to focus on.