My daughter just started sucking her thumb...she has just turned one, strange isn't it?

I was so surprised when my daughter who never took a pacifier or sucked her thumb started doing this a couple of weeks before her first birthday. I thought it was just some teething comfort but now she is full on sucking her thumb...I know most say to leave them be but is it a concern since she has started doing it so late and she has six teeth already?? If so any advice on what I can do to distract her from this??