Custody of child if the mother remarries

Please advise how a young widow with an infant child will cope with the following situation:

Her society and customs and practices require that if she marries anyone, her infant child will be taken away by her in-laws. Her father will not approve of any marriage, even if it is with a Muslim, if he is not from the same country as her, even if the man agrees to keep the child with his mother whom he will marry. The infant will be deprived of his mother’s love if she marries any man of her family’s choice. Staying single means she runs the risk of committing sin (maybe zina) which she does not want. In this situation, as she is an adult widow and not a virgin and has physical needs, can she not undertake a secret marriage?