It’s strongly implied but not quite stated outright.
Old Woman: Rose is my granddaughter.
Natasha: Not a common name, here.
Old Woman: I heard it once. Long ago. From you…
Natasha: I’m here because someone found out. I don’t know who. Or how. I didn’t even think you knew the the truth but the fact your daughter called this baby Rose—
Old Woman: My mother told me what happened to you. I wanted to know why you kept returning, why you would disappear for days into the forest with nothing but the clothes on your back. But I never repeated what she told me.
FWIW, the 2012 Avengers Roll Call update to the OHotMU listed the Natasha as having a (deceased) “unidentified daughter.”