For a non-Catholic or non-Christian, sure. And perhaps a priest or deacon might accommodate a family who suffered an immediate loss and who, for grave reason, needed a Catholic funeral done right away. But I very much doubt any Catholic parish is going to schedule a Catholic funeral during Holy Week for someone who will have already been deceased for over a month by the time of the funeral. If your sister-in-law wants a Catholic funeral for her husband, she will have to take into account not just her own needs but also the needs of the parish.
__________________ "If anyone comes to me, I want to lead them to Him." --St. Edith Stein