You will have to be patient and persist. Having people around with concerns about her speech will likely make her more nervous and stutter. Following a sibling delivery likely a coincidence
Can wait for 6 mnths before intervening in the management
Next Steps
Make speaking a fun activity. Get her to talk about fun things. Have a relaxed environment.
Health Tips
Imp to not react negatively to her stuttering. Praise for proper speech. Not correct or say words for her.