Hi,
The wife should adopt a legal strategy of squeezing the husband economically and mentally by filing the following cases on the husband.
1) File a case of interim Maintenance under section 125 Cr.P.C for the kids and wife. Normally courts will grant interim maintenance of up to 50% of husband salary.
2) File a case of domestic violence( economic , mental harassment. Even having extra marital affair is domestic violence) and ask for protection orders. Since domestic violence is compoundable, the wife can get atleast 5 times the annual salary as compensation.
3) File a case of 498A and dowry (in 498a, the husband may be arrested if not supporting police enquiry).
4) file a case of adultery against the husband and the concubine.
5) file a divorce case on the grounds of adultery and also seek 50% share of property in the name of husband as alimony.
Your friend only needs a good lawyer who will spear head the legal claims of the wife (wife needs to be present in the court only at the time of filing of case and at time of evidence. Her presence will be minimally required).
Once your friend adopts the above mentioned legal strategy, she will be assured of redressal of her grievance on her terms(including monetary) that too with immediate relief.
Hope this helps