Political posturing for the TV cameras. If POTUS activates the Guard, it puts them into a Title 10 status (Federal service). The governor only has authority over ARNG troops in Title 32 status (state service).
She’s legally hosed here, and there’s nothing she can do about it. Except this nonsense.
Or on strictly state status (as opposed to Title 32, which falls under the OTE - organize, train and equip - function)
I think 50-percent of this episode is a test by Trump to get Governors hyped up to insist that they own Nat’l Guard troops, and turn this into a media circus.