about sihr (black magic)

Assalammu alaikum brother

brother i;ve got a question which concerns me alot. once i saw a in a book reverse writing of basmalah, i had to question to whom wrote this, my sister in law next to me said she wrote this due to mistake. to note that she can read the quran and perform salah. now it worries me alot. i know as a muslim to enjoin good and forbid evil. i find this person might be a bit doggy, could a person like her write basmalah by mistakes? is she is sufferening from possession or sihr?
or is he doing sihr?