My sister got pregnant with another man when her contested divorce case is pending

Getting impregnated through her boyfriend during the pendency of the contested divorce case (i e , without getting remarried to him), is not an offence neither her husband can take any legal action against her for her this extra marital affairs.

It is purely her private affair which cannot be interfered by anyone including her husband.

Therefore let she continue the pending divorce case properly because this is totally a different subject to that of the allegations of extra marital affairs against her.

I fully subscribe to the opinion and advise of learned Senior expert Mr. T Kalaiselvan.

No case is made out against your sister lis pendence of divorce proceeding stated to have been filed by her husband, presumably it (adultary) is not a ground in divorce case .