Please Help !!

My Friend got scammed by downloading the Apk.. She got logged out of her WhatsApp and somehow gained the access back.. her WhatsApp was used to send spam and to create groups.. Her normal message app was used to send some Messages to a particular number.. I don't know how they got access to her phone.. But rest everything seems to be untouched.. Any help please .. Should she Reset? Or any further actions would be helpful..