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 ‘alayhi wa sallam, is His Slave and Messenger.
If the pension is given to your grandmother as an allowance that she may dispose of as she wishes, then there is no harm if she gives your mother some of it and you may utilize it by spending it to buy books or anything else. The fact that this pension is from the government and some of it is tax money or gained through both lawful and unlawful sources is irrelevant in this regard; it is considered mixed wealth and it is permissible to utilize mixed wealth according to the most valid opinion of the scholars.
If the government sets certain conditions regarding how this pension should be spent, then these conditions must be followed.
We would like to point out that the grandmother should not favor one of her daughters or sons over the others with a gift unless for a valid reason.
We have previously explained the kinds of pension given by the government and how to dispose of it in Fatwa 90709.
Allaah Knows best.