The marriage under any act other than Muslim personal law with that Hindu woman by your relative is null and void since this person's previous marriage is subsisting and the spouse is living.
Therefore she has no claim whatsoever against her so called husband since her marriage is not legally valid.
Also even if her marriage is recognised, she is not eligible or entitled claim any share in his property by any means.
So let she pose any type of threat or torture him for property, she cannot legally claim anything from him during his lifetime.
All her claims can be properly challenged when it comes before court of law.