Speech is really a science of its own. I would make an appointment for an evaluation with a Speech Therapist just so you can put you fears to rest. Most insurance will cover an eval. I do know the younger a child is when the receive speech therapy, the easier it is to correct.
Has she been nervous about anything? Has she had any accidents lately?
Are you referring to stuttering? If so, it might ease your worries to know that both our son and granddaughter stuttered for a few months at about the age of your daughter. I think it has to do with the anxiety of growing up and leaving Mom for short periods of time - as school, sports, other activities, etc. By the way, both our son and granddaughter learned how to manage their stuttering behaviour - experts claim the best way to handle this is to totally ignore it and not draw any attention to the speech efforts. You might wish to read more about this issue on the internet by googling "stuttering and children" or similar words/phrases in order to educate yourself.
One more caveat - my sister started stuttering at about six years of age and she did not learn how to self-manage this behaviour. Her anxiety behaviours were that of an anxiety disorder and she required help to deal with her fears/anxieties. I say this not to scare you but to educate others who might be reading this posting. I strongly suspect your daughter is of the description in the first paragraph. I wish you the best ....