Urgent question about marriage and culture

See, the situation is somewhat different in this case...

The girl's elder sister got married a year and half ago. She did not request anything for "security," and rather transferred her assets to her husband. She blindly trusted her husband. It later turned out he was already married to someone else without her knowledge. He made her live in Pakistan, took her passport, and went overseas, so she could no longer travel, and he refused to live with her. He also refused to give a divorce. Because of this mistake in judgement previously, the younger sister who I plan on getting married to says that for her own security, and her lack of faith in men in general, despite her trusting me, she finds it necessary to have some backup, unlike her sister who is left with nothing.

This is why I sympathize with her and just wanted to make sure this is normal before approaching my parents. If not normal, is it "acceptable" as a form of mahar, and is it completely extra-ordinary...