This is not allowed. What is required for a woman after her husband dies is to observe an Iddah of four months and ten days from the date of his death if she is not pregnant. If she is pregnant, then her Iddah lasts until she gives birth. It is not permissible for a woman who is in Iddah to get married during her Iddah. After the Iddah for the first marriage is complete, the second husband may do a marriage contract. Men should take the leading role by not proposing women who are on their Iddah period.