You need to have the Prajnaparamita recited for your mother. If it is not possible for you to sponsor the Prajnaparamita, then please read these mantras from the Kangyur and Prajnaparamita for her. [The mantras were sent to the student.]

If you can sponsor the recitation of the Prajnaparamita, then it should be recited by monks at Sera Je Monastery in India. That means you have to make offerings of tea, bread, etc.

Then recite these eight prayers three times, dedicated for her.

Also recite four malas of the Lotus Pinnacle of Amoghapasha mantra: OM PADMO USHNISHA VIMALE HUM PHAT, dedicated for your mother. Recite a few malas each day until you get a good dream about her.