You need to look very hard at Parshat Toldot in order to find Rivka and Yitzchak communicating.
When Rivka is having a difficult pregnancy, she goes to seek out God, and is told (Breisheet 25:23) “Two nations are in your womb and two kingdoms will separate within you. One government will be mightier than the other, but the greater one will serve the smaller one.” Yet we don’t see her reveal God’s message to Yitzchak
When they go down to Grar, during the famine, Yitzchak doesn’t tell Rivka to act as his sister, rather he tells people that she is his sister.
When it is time to bless the twins, Yitzchak calls in Esav without consulting Rivka. She then goes behind Yitzchak’s back, dressing Yaakov as Esav to make sure that Yaakov receives the blessing that Yitzchak intended for Esav.
We finally hear Rivka speak to Yitzchak near the end of the parsha, when the blessings were already given out, after Rivka heard that Esav wanted to kill Yaakov and after Rivka already told Yaakov that he needs to flee to her brother, Lavan in Charan until Esav calms down. None of which does Rivka mention to Yitzchak.
Instead, Rivka tells Yitzchak (Breisheet 27:46) “I am disgusted with my life because of the daughters of Chet. If Yaakov marries a woman of the daughters of Chet, like these, from the daughters of the land, what is life worth to me?”
After Rivka tells him this information (Breisheet 28:1-4), Yitzchak follows her advice:
Yitzchak called Yaakov and blessed him. He commanded him and said to him, “Do not marry a woman of the daughters of C’naan. Set out and go to Padan Aram, to the house of Betuel, your mother’s father, and marry one of the daughters of Lavan, your mother’s brother. May E-l Shad-ai bless you, make you fruitful and multiply you. May you become an assembly of peoples. May He give you the blessing of Avraham, to you and to your descendents with you, that you may inherit the land of your dwelling which God gave to Avraham.
At that moment, it was a life and death situation (even though Yitzchak didn’t know that Esav wanted to kill Yaakov) so Rivka had to speak up and when she did, Yitzchak listened to her.
What held Rivka back from communicating with Yitzchak until that point?
The Netziv, in his commentary, HaEmek Davar, explains that from the moment that Rivka first saw Yitzchak, when she arrived with Avraham’s servant, she feared him.
We see their first encounter in Breisheet 24:64-65:
Rivka raised her eyes and saw Yitzchak. She let herself down from the camel. She said to the servant, “Who is that man walking through the field towards us?” The servant said, “He is my master.” She then took the veil and covered herself.
According to the Netziv when Rivka saw Yitzchak praying, he was like an awe inspiring angel. Even before she knew for sure who the man meditating was, Rivka slipped off the camel out of fear and awe. She covered her face when she realized that this is the man that she would be marrying and she felt embarrassed, afraid and unworthy of being his wife.
The Netziv adds that their relationship was very different from Sarah and Avraham and Rachel and Yaakov where the wives weren’t afraid to say what was on their minds (Sarah told Avraham to send away Hagar, Rachel demanded that Yaakov give her children etc.).
The Netziv concludes that their relationship was set up this way as part of God’s plan to make sure that Yaakov would receive the blessings in the manner that he received them. If Rivka and Yitzchak had communicated like Sarah and Avraham and Rachel and Yaakov, then Yaakov would not have received the blessings in the same way. It was all part of hashgacha pratit, Divine Providence that Rivka first saw Yitzchak like an angel while he was connecting with God.
Yitzchak and Rivka were on a totally different wave length and we will never fully understand their relationship. However, they were both aware that the blessing of the Land of Israel belonged to Yaakov and that intermarrying with idol worshipers was unacceptable.