Is it permissible to answer questions from a girl – with whom there was a previous relationship – regarding matters of her religion, despite the presence of misgivings about showing off (riya’) and feelings of longing for her?

There is no objection to answering the questions of that girl via a text message on a mobile phone, provided that the answerer possesses knowledge of what he is answering and is secure from fitna (temptation/strife) concerning his faith and from relapsing into sins. If the answerer fears fitna for himself and perceives an inclination towards that girl, then he should not answer her and should sever all ties with her. It is preferable for him to change all means of communication she knows. He can also guide her to their website so they can undertake the answering of her questions.