I'm also a licensed Speech-Language Pathologist. Red flag warning signs would include:
--family history of stuttering that lasted into adulthood
--noticeable muscular tension in her face/neck when she is stuttering
--any secondary characteristics (eye blinking, facial grimacing, etc) with the stuttering
--stuttering of a single sound (mm-mm-mm-monkey) or syllable (may- may- maybe) is generally more concerning than repetition of a whole word (the...the...the dog)
--signs that she is very aware and/or embarrassed when she stutters
Things you can do to help:
--slow down your own rate of speech
--add extra pauses in your own speaking
--avoid peppering her with constant questions...comments are more friendly!
--do not interrupt her, and do your best to ensure that others (siblings) don't interrupt either (I know this is challenging!)
--ignore the stuttering and focus on the content of her message--and let her know that you're hearing what she's saying, not HOW she's saying it
If you're not seeing any red flags that I mentioned above, I would try to relax and see what happens in the next couple of months. Good luck to you all, and try not to worry. As you said yourself, this is quite normal in this age group--it's a crazy time of language growth and sometimes their little mouths need a chance to catch up! :)