She did Hajj ifraad with her husband and they failed to do sa‘i
Question

I did Hajj ifraad with my husband, as we are residents of Makkah, but we did not do sa‘i. What must we do? If there is a fidyah (a sacrifice to be offered as a penalty), what organisation can we depend upon to distribute the meat?
Praise be to Allah.Sa‘i is one of the pillars or essential parts of Hajj, without which Hajj is not complete, and the muhrim (pilgrim in ihram) cannot exit ihram completely until he has done it. As for the first stage of exiting ihram, after which everything becomes permissible except intercourse, that is attained by stoning the Jamrah and shaving the head. Then when the muhrim has done tawaf and sa‘i, he has completed the second stage of exiting ihram, and everything becomes permissible to him.
The pilgrim who does Hajj ifraad [Hajj only] is only required to do sa‘i once, so if he does sa‘i after tawaf al-qudoom (the tawaf of arrival), that is sufficient for him.
Based on that, if you did not do sa‘i after tawaf al-qudoom, then you are still in a state of ihram; you have not completed the second stage of exiting ihram and it is not permissible for your husband to have intercourse with you until you exit ihram, by doing sa‘i.
If intercourse has taken place during this period due to ignorance of the ruling, then you do not have to do anything, but to be on the safe side you may offer a fidyah (penalty), which involves slaughtering a sheep, or feeding six poor persons, or fasting three days, which is required from each of you.
But you cannot exit ihram completely except by doing sa‘i.
You must also ask Allah for forgiveness and repent from this shortcoming and heedlessness, for you have not performed the rituals as enjoined by Allah, and you did not ask scholars or people of knowledge throughout this lengthy period, even though you live in Makkah and it is easy for you to do sa‘i.
Shaykh Ibn Baaz (may Allah have mercy on him) was asked: I am a resident of Makkah. I did Hajj last year, and I did tawaf but I did not do sa‘i. What is the ruling?
He replied: You have to do sa‘i. This was a mistake on your part. It is essential to do sa‘i whether you are a resident of Makkah or otherwise. It is essential to do sa‘i after tawaf; after you come back from ‘Arafah you must do tawaf and sa‘i. The one who omitted to do sa‘i must do sa‘i now. If he has had intercourse with his wife, then he must offer a sacrifice to be slaughtered in Makkah and given to the poor there, because he cannot complete the second stage of exiting ihram except by doing sa‘i. So he must do sa‘i now with the intention that it be for his previous Hajj, and he must offer a sacrifice if he has had intercourse with his wife since then. End quote from Fataawa ash-Shaykh Ibn Baaz (17/341).
Shaykh Saalih al-Fawzaan (may Allah preserve him) said concerning someone who did Hajj but failed to do sa‘i because he was unable to walk or to hire a wheelchair: With regard to failing to do sa‘i, this was wrong, because it is obligatory upon you to complete all the rituals, and sa‘i is a pillar or essential part of Hajj, without which Hajj cannot be complete. If you entered ihram for Hajj on its own (ifraad), or for Hajj and ‘umrah together (qiraan), and you did sa‘i after tawaf al-qudoom (the tawaf of arrival), then you do not have to do another sa‘i after tawaf al-ifaadah. But if you were doing tamattu‘ [Hajj after doing ‘umrah then exiting ihram, then entering ihram again for Hajj], or you were doing qiraan or ifraad and you did not do sa‘i after tawaf al-qudoom, then sa‘i remains due from you, so you must go and do sa‘i, seven laps between as-Safa and al-Marwah, with the intention of doing the sa‘i of Hajj. If you had intercourse with your wife during this period, then you must offer a compensatory sacrifice of a sheep, the meat of which is to be distributed among the poor of Makkah, and when you want to go back to your own country, you should do the tawaf of farewell.
End quote from al-Muntaqa min Fataawa al-Fawzaan.
And Allah knows best.