Question: can an old women residing on her own spend her Iddat at her son’s house?
Answer: Due to her old age and her residing alone, it would be permissible for her to spend the remainder of her Iddah at her son's home.
It is also not necessary to begin the Iddah again.
Fatawa Darul Ulūm Zakariyya, Vol. 4, Pg. 325-326
And Allāh alone knows best