Our daughter came home from Ukraine at 3.5yrs old a rabid thumb sucker. We didn't take it away from her because it was literally the only thing she had. BUT the roof of her mouth was awful, she sucked her thumb sideways and it was so curved up we couldn't see the top or back, she made this weird sound when sucking and they evne checked her for cleft palate when she had her MRI! (She has cerebral palsy so the MRI was to see where the brain damage was.)
ANYWAY, we intro'd a pacifier and used the 'no bite' stuff on her thumbs and at first it was just a filler, she would just hold it in her mouth but it did the trick, she stopped sucking her thumb and its only been 4 months since she stopped and started the pacifier and the roof of her mouth has flattened out almost perfectly!
I realize this is a different scenario, but she's not hooked on the pacifier. She uses it to fall asleep and then I put it up and thats it. She doesn't use it any other time. I think if it was controlled (ie just in bed) then it would be fine.
I used to be os against pacifier use, my boys had them from birth and also nursed but both lost interest in the pacifier around 8/9 months, so it was never an issue. BUT with her, its important to not just take something away that she has relied on and been her only constant for years.
I don't think it would be a terrible thing, honestly. As long as you didn't let her drag it around in her mouth all day.