Does a mother's frequent prayer against her daughter, saying "may you be unlucky" (طيح سعدك), have any relation to the delay in her daughter's marriage, and does it mean that she will not get married?

The delay in marriage is not necessarily due to a mother's supplication. If Allah has decreed a marriage, it will happen. It is recommended to supplicate frequently and to take the necessary means. There is no harm for a woman to offer herself for marriage, within Islamic guidelines, or to seek help from trustworthy individuals. It is obligatory to advise the mother not to supplicate against her children, to be dutiful to her, and to avoid displeasing her.