Confused about the adding a line after tiered data plan launches

Absolutely not.

Is she on a Verizon account of her own? If so, you can do an Assumption of Liability, which would basically take her existing line off of her account and put on yours. It doesn't break a contract, so no fees... just transferring it from one account to another.

 

Just keep in mind that if she chooses to add data on her line in the future, she will not have the unlimited data. Just because you have unlimited data does not allow her to get it.

It won't effect your unlimited data, but she'll have to choose a tiered plan.