Reversing BBM data transfer

I downloaded BBM to my new device, a windows phone (Nokia 520), while my old Blackberry (Curve) is used by my mom. I accidentally sign in with my old username and password and all of my mom's BBM data is transferred to my new phone. How can I reverse this? I already reinstalled new BBM and sign up under new email, but the damage on my mom's phone is still there. Please help. Thank you.

Sign in using the same credentials on your mom's phone so she can have her account back. The contacts are linked to the BlackBerry ID.

Thanks so much! It works!