what's the meaning of "hold strong for sb"?

Serafina’s daughter searched her dog-eared address book, picked up
the telephone and dialled the number of her only aunt two hundred
miles away, tucked in a tiny white cottage called The Limit.
‘If you want to see her, come now,’ she said.
Mary held strong for her sister’s child, fighting the stone suddenly
lodged in her throat. ‘Is she very bad?’