My kids all reacted differently to pacifiers. My eldest found a great deal of security in her pacifier and rarely went without it. Once she was 18 months, I chose to limit her use. She was allowed to have it at naptime and bedtime. Later, she was only allowed it at naptime. And then only when she was really ill or sleeping in a strange place (which was VERY rare.) She now has no need for it at all. And her teeth are straight and she talks like every other kid her age.
My second child, nursed for 14 months and she rarely used her pacifier so when 18 months came around, she had no need for it anymore. She gave it up willingly.
My youngest is 2 year old and has his at naptimes and bedtime only. But I don't think he will struggle too much when it is gone. Even now, we talk about how he doesn't need it anymore.
Along with limiting the usage time, I also tell them often that they are big kids and they don't need it anymore. I reinforce that they want it and that is okay, but they really don't need it. Eventually, I think the point gets across without to much hassle.
But the other aspect is, if you take it away and she throws a tantrum, DON'T GIVE IT BACK. I believe it giving it back would set a pattern into motion that would be a HUGE issue later.
Also, it may be hard for her to give up the pacifier (aka one source of comfort and security) when her brother has one.
I know you can do this. Eventually she will get over the loss and understand she is a big kid now.