Don't worry about it.

At ten months old, there isn't much you can do to stop her from sucking her thumb, other than handing her something interesting to hold onto. She'll most likely stop the habit on her own.

Keep this in mind: if it becomes painful, she won't do it.

My advise is don't worry about it for now. By all means, don't say anything to her about it. If it bothers you, just distract her with something more interesting when you notice her doing it.

Andy, Father of eight.