Do not worry. Now the 498A and dowry act concept has been diluted. Now the police cant book cases against you mechanically. There are supreme court Judgements on this point. If she really files the case against you and your close relatives, contact me through Kaanoon.com. I will help you.
Regarding house is concerned it is in your name. Is it your self acquired or ancestral. If it is your self acquired, nobody can claim your property. You have full rights.
Regarding threatening that she will commit suicide and kill her 2 years daughter, you should get alert. You, yourself, your mother and other relatives associated with this issue should give a legal notice (through registered post and emails and SMS) to your brother's wife, asking her to withdrew her claim of asking your property and also withdrew threatenings of killing herself and her two years old daughter and to mend her ways and to come to scences and to maintain harmony and peace in the family. This will save you to large extent, if she commits suicide and may be with suicide note. You can come out of the criminal case easily.