People are very uneducated and this person was either not exposed to other stutterers before or taught anything about it. Im sorry you had to go through that. Just know she is uneducated and u can use this as an opportunity to teach her about stuttering. she might encounter someone else who does in the future and because of your interaction will be a bit more compassionate. You may have made a positive impact for the next stuttering person and not even know it but I know it was probably still very hard to take regardless.