What cmguy said. Fridge magnets, letter blocks, stamps, alphabits cereal, alphabet pasta, etc. Maybe try paint? DD loved a big easel with rolls of paper, chalk on the driveway, "painting" with water on the driveway or side of the house, shaving cream on the wall of the tub/shower. Finger paints or "painting" with pudding are also fun.
Our DD was similar, and at 3 went to a Montessori- many of the first activities are designed to support the early motor skills needed for writing. We did lots of clay and play-do type stuff, DD hated pin-punching but it has a similar goal, sewing cards and lacing-type activities, eventually moving to real sewing, lots of scissor-crafts, Lego and other building requiring hand strength- all can be helpful (though frustrating to a kid whose motor lags behind their brain).
