It is timing right now more then anything. It is very normal at 2.5 to throw tantrums, have sleep disrutpion. Even without changes.
Change takes time. Do not sleep with her at night, it is fine to reassure her but encourage her to be the big girl and if you continue this pattern it will become a very hard habit to break.
Let her cry for 5 to 10 minutes, if she continues, go in, get kisses and hugs and tell her it is time to sleep. During the day explain how sleep helps you grow and stay healthy. Just in a matter of fact fashion.
Explain too, if she gives up naps, then she has to go to bed very early and let her choose. My son did this at about almost 3 and he had to go to bed at 6:30. After a few nights he preferred not to do that so he started napping well again for a few more months then gave them up all together. He had an earlier bedtime when the naps stopped and he was finally okay with that but I let him decide.
Consequences and not changing her routine is the best thing you can do for her. You can give her some extra TLC but at the same time don't coddler her anymore then you did previously before the baby. Have her get a baby doll and help her baby when you are helping your baby. Get her photo album out of when she was that little and explain how much she needed you at that age and explain how babies don't talk and need lot's of extra attention right now.
Just give it time.
It can throw them off a bit, but keep things consistent for her for added security. It is very normal at her age to start with tantrums anyway, my daughter didn't have her first one until 3 and it was about the same time her little brother came along, it wasn't jealousy as so much the age for the frustration fits to start. Just keep things structured, praise her for the good behavior however have consequences for the bad behavior too. Letting her know that things are still the same and rules still apply.
Biggest thing is to not sleep with her to get her back to sleep, you need your rest and it will get better.
Hang in there, Congrats on your new baby!