1. First of all your niece should decide whether to go for mutual consent divorce or contested divorce.
2. In case she decides to go for MCD, she has to convince her husband to agree for MCD.
3. In case she decides to go for contested divorce, let her file a petition in the court against her husband for Restitution of Conjugal Rights. If there is no positive response from her husband for RCR, let her file for divorce using this reason, as also domestic violence, mental harassment.
4. Better to convince her husband to agree for MCD, wherein the divorce would be less stressful and can save time, effort and money and also to avoid long litigation and your niece can move on with her life just after 6 months' of filing for divorce and also in addition to alimony to be decided by the couple, other things like return of articles, division of assets and finances and money towards child's education, etc..and agreeing for one time lumpsum settlement.
5. In case of contested divorce which is a long drawn procedure, the alimony of one time settlement depends on various factors like, whether your niece is employed?, What is her salary, Whether her husband is employed or is he doing business or is a professional and what is his monthly income etc..