Hi A.Z.,
This is a totally normal phase, but you can actually cause her to develop a stutter by what you're doing. Model slower speech, but don't anticipate and correct her. Calling attention to speech patterns can cause a child to focus too much on the individual sounds and how they're speaking. This can cause a negative feedback that impedes the child's natural fluency. For more background on this, look up the "the monster experiments" that were conducted in the 1920's.
Also, please find a way to incorporate English into your daughter's everyday activities. Kids this age have no problem learning two languages at the same time and at the same rate as learning a single language. Your daughter needs to not only speak fluent English by the time she enters Kindergarten, but should also have acquired some English reading skills. Because of the "No Child Left Behind" approach to education, kids who do not enter Kindergarten with these skills can be at a substantial disadvantage for several years as they try to catch up. This disadvantage can extend to every aspect of academics, as reading is the backbone for every subject -- even math. This past year, I started working with 1st grade children who were struggling with reading (one of whom came from a household where only Spanish is spoken). Part way into the year, I started tutoring them in math as well. Not only were they struggling with the concepts, but most of the problems were "word problems", which compounded their difficulties.
I am not suggesting that you stop speaking Armenian to her -- you absolutely should! Just please consider enrolling her in an English immersion preschool by the time by the time she's 3 or 4. Another way to handle this would be for one parent to speak to her only in English, and the other only in Armenian. I have friends who have raised their children bilingually this way very successfully.