get her some flowers and tell her how much you appreciate her and what she does. its really the thought that counts, not how many presents you give her or how fancy your present is to her, its about letting your mom know how much you care about her her and how happy you are to be her son... but that's just my opinion. really just do what YOU think she will appreciate that most. hope i helped.
For mothers day, you can get your mum a necklace, flowers, spa basket, ceramic lanterns as show of how much light she has brought to your life, wine cork candles, or anything that she has always sung that she will buy but she has never. You can also buy her a pendant, a bath robe, or get an engraved wood, with a nice poem on it. For more ideas on this, visit http://www.gifts.com/ideas/mothers-day.