If she’s still on maternity and is going back to a job (regardless of how long she’s going to take off) then she’s eligible. She probably just needs to state on the application that she’s going still employed wherever she was/is. If she decides not to go back then she can change it then. I’ve just done this. If she isn’t working but her partner is she’ll be entitled to 15 hours.
My understanding is if on maternity leave still qualify ?