The White Collar actress welcomed her first child with husband Brady Smith in June 2010.
Asked how she and Smith find time to themselves since becoming parents, Thiessen told People: "My mother. My father. They're perfect and they're built in. [They allow us] a night for just the two of us."
Thiessen also said that, with the responsibilities of being a working mother, she could not raise her child without help.
"I'm not doing it alone. I have my mother who helps out a lot with my daughter, and I have my husband," she explained. "They make it so much easier for me to be able to… work and to do the things that I want to do, and to be able to spend as much time as I do with [Harper]."
Thiessen recently commented that Harper is no longer a baby and has had many milestones in recent months.