Praise be to Allah.
Stoning Jamrat al-‘Aqabah is one of the obligatory actions of Hajj.
If someone is unable to do it, or it is too difficult for him, it is permissible for him to delegate someone to stone it on his behalf.
Ibn Qudaamah (may Allah have mercy on him) said: If a man is sick, or detained, or has an excuse, it is permissible for him to delegate someone to stone it on his behalf." (Al-Mughni 3/257).
Shaykh Ibn Baaz (may Allah have mercy on him) said: There is nothing wrong with delegating a proxy [to stone the Jamaraat on one’s behalf] for one who is sick, or a woman who is unable to do it, such as one who is pregnant, heavy or weak, and is unable to stone the Jamaraat." (Majmoo‘ Fataawa Ibn Baaz 17/301).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If the pilgrim is not able to stone the Jamaraat, whether that is due to old age, or sickness, or pregnancy, or a man or woman who is blind and it is too difficult for them, then in this case there is nothing wrong with delegating someone to do it on one’s behalf, because it is a case of necessity." (Majmoo‘ Fatawa Ibn ‘Uthaymeen 23/119).
If this woman appointed someone to stone the Jamaraat on her behalf because she was old and tired, and she thought that she would never be able to reach the Jamaraat because they were too far away, she does not have to do anything to compensate for that.
If someone delegates a proxy because of an excuse, then that excuse ceases to exist, even if that happens within the timeframe [for stoning the Jamaraat], he does not have to repeat it, according to the view of a number of fuqaha’, and he may stone the Jamaraat himself on the remaining days.
An-Nawawi (may Allah have mercy on him) said in al-Eedaah (p. 322): If the proxy stoned the Jamaraat, then the excuse of the one who appointed him ceases to exist and there is still time left, then the correct view is that he does not have to repeat the stoning. End quote.
Al-Ameen ash-Shinqeeti (may Allah have mercy on him) said: If the proxy stoned the Jamaraat on behalf of one who was unable to do it, then the excuse of the one who appointed him ceases to exist and the days for stoning the Jamaraat have not yet ended, then we have noted above the view of Maalik in al-Muwatta’, that he should make up everything that the proxy did on his behalf, and he must also offer a compensatory sacrifice. But some of the scholars said that he does not have to make up what the proxy did on his behalf, because the action of the proxy is like the action of the one on whose behalf he did it, so what is obligatory has been fulfilled, but it is recommended to repeat it. This is the well-known view in the madhhab of ash-Shaafa‘i. But there are scholarly views concerning this issue other than what we have mentioned here." (Adwa’ al-Bayaan 4/474).
According to this view, this woman does not have to do anything, although it would have been better for her to repeat the stoning of Jamrat al-‘Aqabah.
And Allah knows best.