If you have her at the beach, try just walking her into the water with you, and not making a big deal out of it. She's still a baby, she has a lot to learn about the world. You could also carry her in while she is still small, to a point where it is deep enough that she'll have to swim, and set her in the water and praise her when she starts swimming, so she's know she can control herself in the water, and that swimming is an okay thing to do!