Adverse possession usually realates to squatting. If this woman has neither lived nor maintained the property in the last 13 years, then provided she does not have the legal title to it, the house should belong to whoever your brother left it to in his will, or if he did not leave one, then his estate will follow the rules of intestacy.
If this woman has maintained the house for 12 or more years and the 'real' owners have not made any positive steps to reclaim the house, she may well have a right to the house under adverse possession