They found nothing criminal but they settled on that I was carrying some of her money(not sure what kind of crime that is?).
Possibly they suspected "structuring" where one carries money so the other has less than $10,000.
Joe has $2,000 in currency. His wife Mary has $11,000 in currency.
Mary hands over $3,000 to Joe so she will be carrying less than $10,000 and avoid declaration. That's structuring.
A recent famous case of structuring involves former House Speaker Dennis Hastert. He was being blackmailed by his own former students that he had sexually molested in the past. Hastert paid off the blackmailers by withdrawing cash in increments of less than $10,000 from his bank, thus avoiding the FinCen reporting requirements,. When this came to light, Hastert was prosecuted for structuring. The statute of limitations on the sexual misconduct had already expired.