Pham Thi Hanh, 35, is being investigated for procuring, the police said Thursday.
In March police officers raiding a hotel in Yen The Town found three girls, aged 17-18, prostituting in two rooms. They said they had been sent to the hotel by Hanh.
She reportedly used several schemes to lure the girls into sex work, and paid them half of the VND3 million ($127.71) customers paid, keeping the rest for herself.
Procuring is punishable with a jail term of up to 15 years.