It depends.  You might have to file her as a part-year resident for two state returns, but it will depend on the state in question, because she may be in a state now that does not tax her income.  If both states tax her income (likely only pension, but some have investments also), then she will need to file a part-year return for each state.  If only one state taxes her income, then she only needs to file a part-year return for that state.

The purpose of the part-year return is to report and separate the income she made while living in that state so that not all of her income is taxed there.