Erin on the other hand, we should see a lot more of. She is Markus' right hand and probably the number two person in power and influence around TM. Erin is a very determined and through in her work. She has an incredibly strong loyalty to Markus.
Even though her character may have initially sounded quite similar to Sarah, they are not the same. Our original assumption that Erin replaces Sarah appears to have been false.