Praise be to Allah.
What appears to be the case is that her Hajj is valid, because it is as if she used to say: I am entering ihram for what the people are entering ihram for, and it is permissible to enter ihram for what someone else enters ihram for. The Prophet (blessings and peace of Allah be upon him) said to ‘Ali ibn Abi Taalib during the Farewell Pilgrimage, when he came from Yemen with Abu Moosa al-Ash‘ari (may Allah be pleased with them both), “What have you entered ihram for?” ‘Ali said: For that for which the Messenger of Allah (blessings and peace of Allah be upon him) has entered ihram. And he said: I have brought the sacrificial animal with me. So he told him to make it qiraan [hajj and ‘umrah together]. As for Abu Moosa al-Ash‘ari, he also said that he had entered ihram for that for which the Messenger of Allah (blessings and peace of Allah be upon him) had entered ihram, but because he did not have a sacrificial animal with him, the Prophet (blessings and peace of Allah be upon him) instructed him to make it ‘umrah (and then follow it with Hajj), because tamattu‘ [‘umrah followed by Hajj, exiting ihram in between] is better than qiraan.
Undoubtedly this woman – according to what appears to us to be the case – entered ihram for that for which the people entered ihram, and said, I will do what the people do. But what a person must do, when he decides to do an act of worship – whether it is Hajj, fasting, giving charity or anything else – is to learn about it before he does it. If he comes after having done it and says: What was the ruling? this is undoubtedly contrary to what is preferable. End quote.