What do you think of this name for a little girl?

No, it sounds silly. Ellie sounds too babyish and nickname-y to begin with but paired with the last name Ellis it's just terrible. I would really try to find a name that does not start with the "elle" sound but, if you are dead set on something like that then at least use a full name like Eleanore or Eliana so that the flow between first and last name is a bit improved and so she has a more adult sounding name to fall back on when she gets ped the age of 5.