Well there are ways of talking to people.
There is aggressive, as in ' what tf are you behaving in such a horrible way to my DD for?
Or assertive, as in ' I would like to talk to you about something that is troubling me and I hope by talking about it, and with your help, that we can resolve the situation.
Is she your older sister?
Otherwise the advice is to keep your DD and your sister apart if you can't protect her, until they have both grown up a bit.
Your sisters behaviour isn't at all nice. Your DD is only four.
You NEED to protect your DD decisively from your sister, otherwise your DD will know that you put your sisters feelings before hers.
My DM didn't protect me from her sisters. She allowed them to be very negative about me when I was young, to my face and about me. I lost respect for my DM big time.
Fortunately, I grew up to be smarter and richer than any of their daughters so I had my revenge. However, I never forgot my DM standing by whilst her sisters insulted me. They were a pretty witch like bunch.