Urai Hahha, 42, was arrested at a rented room in Tambon Patong of Krathu district in Phuket.
Acting on a tip-off, police raided the room and found 316.52 grams of crystal meth and a K75 grenade in her room.
The woman said she had bought the drug from Hat Yai in Songkhla to resell to teenagers and tourists in the Patong area.