When reading through Parshat Toldot, one may conclude that Rivka was a prophetess. In fact, we find in Breisheet Raba and Yalkut Shimoni that all of the foremothers, Sara, Rivka, Rachel and Leah were prophetesses.

If Rivka was a prophetess then why is Sara the only one of our foremothers who is listed in the Talmud, Megilla 14a:

Seven prophetesses- Who were they? Sara, Miriam, Devora, Chana, Avigail, Hulda and Ester.

The Taz (Breisheet 29:34) explains:

Rivka, Rachel and Leah are not included in the list of prophetesses (Megilla 14a) since the women listed there all had prophecies about someone else. For example, Sara’s prophecy was that Yishmael would not inherit with Yitzchak. Rivka, Rachel and Leah’s prophecies were about what would happen to them personally, not what would happen to others and therefore they were not included on the list even though they did have prophecy.

We see Sara’s prophecy in Breisheet 21:10:

She said to Avraham, “Drive out this slave-woman and her son, for the son of this slave-woman will not inherit with my son, with Yitzchak.”

Avraham was worried and therefore God told him (Breisheet 21:12):

“Do not consider this wrong in your eyes on account of the boy and your slave-woman. Regarding all that Sara tells you listen to her, for only through Yitzchak will seed be considered yours.”

Rashi comments that we learn from here that Avraham was inferior to Sara with regard to prophecy.

Since Sara was sure of her prophecy, she spoke up and told Avraham what needed to be done.

Dr. Tamar Frankiel points out in her book, The Voice of Sarah:

Sarah saw the character of Yishmael and had him banished from the household. Rivka saw the character of Esav and contrived to have his father’s favor taken away, then separated him from his brother by sending Yaakov far away…Rivka’s story adds something new. The rivalrous sons were both her own sons, not children of two different wives; and she had to send her favorite son away, not, as in Sarah’s case, the misbehaving one…

Rivka, as far as we see in the text, did not discuss the prophecies that she received about her children with Yitzchak. Instead, she took action behind the scenes to make sure that Yaakov would inherit the Land of Israel.