Assalaamu alaykum wa rahmatullaahi wa barakaatuhu Brother. We do not celebrate birthdays, but on special occasions such as these, my mother's constant advice is to pray two units of voluntary prayer and/or read Surah Yaseen and make special supplications to Allaah. I do not know whether this is an innovation or not because after all, she is just asking to pray for goodness and blessings in the form of prayer and supplication. Is it ok for me to obey her? I quite hesitate as I am not sure about the innovation part and hence thought to seek a clarification. May Allaah reward you for your time...

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, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

Some scholars stated that it is a form of innovation to perform a certain act of worship on a certain time without evidence from the sharee'ah to prove this specification. Ash-Shaatibi defined religious innovations as follows: “And it includes specifying certain times with certain acts of worship that were not legislated by the sharee'ah...” [Al-Iʻtisaam]

Performing specific acts of worship such as prayer, specific supplication, or reciting a certain soorah on particular days such as birthdays or the like is a religious innovation. The Prophet, sallallaahu ʻalayhi wa sallam, said, “He who introduces an innovation to this religion will have it rejected (by Allaah).” [Al-Bukhari and Muslim] Another version of the hadeeth reads, “He who does an act which we have not commanded will have it rejected (by Allaah).” [Al-Bukhari reported it as a Mu’allaq hadeeth (i.e. a hadeeth whose whole chain of narrators is omitted), but Muslim reported it with a complete chain of narrators]

It is impermissible for you to obey your mother when she commands you to do any of that. The Prophet, sallallaahu ʻalayhi wa sallam, said, “There is no obedience to a human being in what constitutes disobedience to Allaah.” [Ahmad; Al-Albaani: authentic] Please, refer to fatwa 84942.

You should clarify the religious ruling to your mother and politely apologize to her in a gentle manner.

Allaah knows best.