In this case, I agree with your counselor. It isn't ideal, but neither is a split family (speaking from a lot of experience with a step family both as a child and a parent).
Ime, the best thing for your ydd is to spend a lot more time with her dad and sister. If she adjusts now, before she can really remember, to a life of one week with each parent, then she won't have a difficult transition later. Her dad is every bit as much her parent as you are, and dads are equally important. Unless one parent is unfit, I totally advocate for equal time, no matter the age.
Many things to many people.