Dorothee Burkhart appeared before a court in Los Angeles apparently unaware her son's being held over a wave of arson attacks in the city.
She's accused of a series offences in Germany, including failure to pay for breast enlargement surgery in 2004.
Prosecutors say she faces possible extradition over fraud allegations although no formal request has yet been made.
SOUNDBITE: U.S. Attorney's spokesman Thom Mrozek saying (English):
"Ms Burkhart is being held after an arrest warrant was issued in the United States, after Germany asked that she be taken in to custody. What this indicates is that we are at the beginning of an extradition process. Germany has indicated that they want to bring her back to Germany to face the 19 counts of fraud filed against her."
Burkhart's son Harry is being questioned over 53 arson attacks in Los Angeles during the New Year holiday weekend.
He was arrested on Monday.
A man resembling him was seen on surveillance footage leaving the scene of several fires.
Paul Chapman, Reuters