Can a US expatriate who has not filed taxes in the US return to the US for a visit?

Here’s the story…

My family emigrated from the US to Canada when I was an infant and my older sister was about 4 years old. Nobody renounced US citizenship but we did become naturalized Canadian citizens when I was young. I moved back to the US about 20 years ago, but my older sister and parents remained in Canada.

Several years ago, my mother said she had seen something in the news about US expatriates who had not filed non-resident tax returns were being stopped at the border when trying to visit the US. I don’t know exactly what she was referring to, but I believe it was the Foreign Account Tax Compliance Act.

She does have a social security number and a US birth certificate, and her Canadian passport lists a US city as place of birth.

My question is simple. Will my older sister, who has lived and worked in Canada all her life but who has not filed anything with the IRS or other US government agency, encounter any difficulty when flying from Canada to the United States for a visit?