As salamu'alaykum I am a brother whose mother is christian, my father is muslim but married a christian. My question is sometimes when i speak with my mother she tells me may God make this and that for you she said it just like other muslims say when they pray for someone i want to know if it is permissible for me to say ameen because it may make her sad because every time she says these wishes i don't answer and she surely expects me to say ameen. JazakumuLlah khayr

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

It is permissible for you to say Aameen when your non-Muslim mother prays for something good for you. The commentary of Al-Jamal reads: “Shaykh ‘Umayrah quoted Ar-Rooyaani as saying that it is not permissible to say Aameen when a non-Muslim supplicates because his supplications are not accepted, as Allaah says (what means): {And the supplication of the disbelievers is not but in error [i.e. futility].} [Quran 13:14] … However, it is permissible to say Aameen or rather desirable to do so when he [a non-Muslim] supplicates for himself for guidance or supplicates for us for victory, for instance, but it is forbidden to say Aameen if one does not know what he supplicates for as he may be supplicating for a sin.”

Finally, you should know that the best act of kindness to your mother is to invite her to Islam and endeavor to guide her to it. You may make use of the following Fataawa clarifying that Islam is the true religion: 111063, 81979,  88906, 88051 and 86091.

Allaah Knows best.