Try showing your daughter what a pleasant voice sounds like. If she says, "mummmmmmmyyyeeeeeeee" just say to her, "Say it this way please, 'Mommy.'" Then when she does it the right way, immediately use the CLeaR Method- Comment, Label, Reward (see Raise Your Kids without Raising Your Voice for details). You'd say something like, "That was just the right way to say it! You used your BIG GIRL voice. I think that deserves a (name a specific reward like "a big kiss" or "a chocolate chip cookies" or  "a special story right now" or whatever else will really please your little one. Follow the same procedure for 4 or 5 times, each time offering the reward step. After that, begin to thin out the reward by using the first two steps only (Comment & Label) and skipping the reward one time, giving it the next, skipping it two times, giving it once, skipping it three times and giving it only one last time. See how this works.    Sarah Chana