:salam2: sis when u have these questions, i believe that it is best if you ask a sheikh. but from what i know, you are allowed to pray for non-muslims that Allah guides them but when they die you cannot make dua for them at all. This is because once the Prophet salAllahu 'alayhi wasalam sat in front of a grave, that was the grave of his mother-Amina. He started weeping and the sahabah saw him weep, so they too began weeping and then the prophet asked Allah as to whether he can make dua for her because u have to remember that Amina was not Muslim. But Allah SWT did not allow it.
If ur question is that are we allowed to ask non-muslims to make dua for us then this is a bigggg noo noooo. why? think...because they commit shirk and don't believe in Allah and rely on false gods besides Allah The One, The Absolute. Then thats shows that if u ask them to pray for u and u believe that their prayers will be answered, then u yourself can fall into shirk, the major sin which Allah SWT does not forgive. Furthermore, the prayers of the non-believers is not answered, their prayers are in vain; whereas, the prayers, the supplications, the duas of the Muslims is answered if Allah so wills.
I think you, and not just u but me and all Muslims should study Tawheed in depth so that we understand the Oneness of Allah.
Your friend that told u this, next time ask her to show u proof from the Qur'aan and the Sunnah, i.e. Hadiths, or do not believe her. Ask her to bring her proofs if she is truthful. Otherwise how will we know what is rights and what is wrong??
I am no way a scholar, noooo and the answers I gave above are not backed up with the Qur'aan and the Sunnah, i.e. i didn't provide any references, I hope it helped and gave u an idea of what I'm trying to say, however you should still definately contact a sheikh ASAP.
May Allah have mercy on me if I said anything wrong. ameen.
