For my DD this stage passed when she was around 6months and could put her own dummy in. Although I was pulling my hair out before that and seriously considering ditching it. I'm glad I didn't now though cos DD is a fab sleeper at 8mo.
Lots of babies go through a phase of frequent waking at that age, so you might find that even if you ditch the dummy, she'll still wake. Tbh if it's settling her straight back to sleep I would keep it for an easy life! My DS is 7.5mo and still has his dummy at night and still wakes for it sometimes - if it's nearby he'll put it in himself but a lot of the time he's lobbed it out of the cot!
I know this goes against the flow of what others have said but I took my DD's dummy away at 4 months (17 weeks to be precise - I remember it well) and I was so stressed by the thought of doing it, but didn't want a. to be getting up in the night or b. have the stress of doing it when they are older and less compliant! And, it was the least stressful thing of the lot.
I was prepared for 3 nights of hell but really she didn't miss it really at all. Naps were slightly iffy in that she cried a bit before falling asleep but not masses and the nights were as they were before. I have to say I was hoping for a miracle cure for the night wakings but no such luck, but we went from 6 times up in the night to 2 or 3. I'm also glad I don't have the issue to come in future years/months.
She's now 10 months and still not a fantastic sleeper but since she found her thumb (6 months) and learnt to sleep on her front she's a lot better.