Neither of mine had dummies, so no personal agenda here
It's something that gives the child comfort, and there seems to be opinions in here that it's bad for a child to need comfort. That it's good to get rid of comfort objects. Why is that I wonder, eventually they will be dropped, and some people keep them, what's the problem with that. There is nothing virtuous about not needing comfort, the child might go on to suck her thumb, or just be less secure. If the mother wants to help the child wean from it then best to do it gradually at the child's own pace, if the child will be distresses, does it help to think about her reaction as distressed rather than a tantrum, then mum is right to consider her child's feelings and work with her how to do it with no distress. Not all outbursts are tantrums
Many of us gain comfort from things such as having a cuppa when we've had a hard day, some if you might have a wine. How would we like it if someone said no more cups of tea, you get comfort from them and you are old enough to just have a drink if water when you're thirsty. Or no more Horlicks or ovaltine at bedtime, it's just a habit and you don't need it any more.