The Gemora writes that a woman may not get married for 24 months if she is feeding a child, because if she gets pregnant the child will not have what to eat. Nowadays, that there are baby foods can a woman remarry in the 24 months?
The halacha as written in the Shulchan Aruch (Even HaEzer 13,11) is that a woman may not marry for 24 months after the birth of a child from her previous marriage. There are circumstances, however, when she is permitted to marry earlier- eighteen months from the time of birth or even earlier (Shut Iggrot Moshe Even HaEzer 2,9; Even HaEzer 4, 49). Considerations that are taken into account are the welfare of the child, whether an adequate amount of money has been guaranteed the child through his 24th month, and the amount of time it is customary to nurse a baby in the country where the woman is living. If your question is not merely theoretical, you must consult a rabbinical authority who- knowing the mother and her circumstances- can address these considerations.