According to ISLAM Way, celebrating Mother’s Day is NOT permissible for Muslims because it is an innovated festival by non-Muslims which the Prophet and his companions did NOT observe. It is also an imitation of the kuffar (filthy unbelievers) from whom we have been commanded to differ.
Arab News A US-based nonprofit group is marking this American Mother’s Day in a special way — by sending greeting cards to Muslim and immigrant mothers. Forward Together is distributing 15,000 customized cards to these mothers across the United States this month, the group told the Huffington Post.
I guess the card below would be a good one to send to your mother if she is one of the four wives of your Muslim father: