Query

Stricktly speaking she will not exemption of HRA u/s 10(13A) as the rent paid in this will be zero since after the death of her mother in law , property would have been transfered to her husband and her husband 's brother in which she is also having a share...

so she cannot take....

however if she can prove that she is paying rent in that case she can take...

Yes she can continue to take such benefit. Because the interest in such property is held by her husband and her brother-in-law not by her. But she needs the consent of her brother-in-law with respect to such benefit.