According to a letter Leanne wrote to Jared, Leanne met and trained with Emmett when they were 18 years old. They were sent to America when they were 22 and Jared was born shortly after.
Her Virginia driver's license had a birthday of August 22, 1959, but this would have been obtained using the birth certificate of the real Leanne Connors and therefore is not her real birthdate.
Leanne lived with her family in America about two decades (as Jared is a senior in high school); in that time, she and her husband most likely completed many missions as KGB agents. They were able to blackmail Andrew Larrick into becoming an informant during that time.
Leanne appeared to be close to Elizabeth, the two of them shown to have gone on multiple missions together and discuss their personal lives. She asked Elizabeth to give Jared a letter that explained her Soviet roots if anything ever happened to her and Emmett. ("The Walk In")
In January 1982, the Connors and the Jennings team up to gather intel from Roy Oatway. Afterwards, the two couples express the desire to see the others’ children and plan to meet at a fair in a few days. The peaceful family outing takes a dark turn when, after obtaining a drop from one of Emmett’s informants, the Jennings stumble upon a murdered Emmett, Leanne, and Amelia in their hotel room. ("Comrades")
Although many suspect Larrick as the killer, as the Connors were blackmailing him, Jared later reveals himself as the real killer. The Center had attempted to recruit Jared into the KGB, something his parents did not agree with, and he kills them in his anger and misunderstanding. ("Echo")
Elizabeth burns the letter Leanne told her to give to Jared in order to spare Jared’s feelings, not knowing he already knew they were agents. ("Comrades")
Your father and I love you more than you can possibly imagine, and, that is the reason for this letter. We want you to know who you really are, want you to know your history and your family, no matter what anyone else might tell you.
I was born in the Soviet Union in a town called Gdansk. Your father was born in the Black Sea, in a fishing village called [...]. At age 18, we were brought together as teenagers by the KGB, and trained as spies. At 22, we moved to America as a married couple and you were born.
We have lived and worked as spies for the KGB until now, sworn to secrecy for your own benefit. You were meant to grow up an American boy with no knowledge of your Soviet roots.
But if you are reading this letter, than the unimaginable has happened. All of this must come as a surprise.
Our love for you is the most true and constant thing I've ever known.
Love, Mom & Dad.
-- Leanne's letter
Leanne was known to be a loving mother. Both Jared and Elizabeth repeatedly said Leanne was a great parent.