The woman who is in iddah following the death of her husband has to stay in her marital home until her iddah ends.
It was narrated from Abu Saeed al-Khudri (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said to his sister al-Furayah bint Maalik (may Allah be pleased with her): Stay in the house in which the news of your husband's death came to you, until your iddah is over.
Narrated by al-Tirmidhi, 1204; Abu Dawood, 2300; al-Nasaa'i, 200; Ibn Maajah, 2031. Classed as saheeh by al-Albaani in Saheeh al-Tirmidhi.
It is permissible for her to go out of her house during the day for necessary purposes, such as to go to the market and buy what she needs, or to go to work, and so on.
But at night she should not go out except in the case of necessity, such as if thieves attack her house and the like.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
The woman who is in iddah following the death of her husband has to wait for four months and ten days, and she should avoid adornments and perfume on her body and clothing; she should not wear adornments or put on perfume or wear fancy clothes. She should stay in her house and not go out during the day unless it is for a need, and she should not go out at night except in the case of necessity.
It is permissible for her to do everything that is permissible in times other than iddah, such as speaking to any man she needs to speak to if she is properly covered, and so on.
What I have mentioned is the Sunnah of the Messenger of Allah (blessings and peace of Allah be upon him) which was the practice of the women of the Sahaabah when their husbands died, and it was the practice of the wives of the Prophet (blessings and peace of Allah be upon him) too.
Majmoo al-Fataawa, 34/27, 28
It is not permissible for her to go out of her house for the purpose of receiving condolences, as mentioned in the question, because if it is not permissible for her to go out for Hajj during the iddah period, it is more appropriate that she should not go out to the house of her husband's father in order to receive condolences.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) was asked about a woman who intended to go for Hajj with her husband, then her husband died in Shabaan. Is it permissible for her to go for Hajj?
She does not have the right to travel for Hajj during the iddah following her husband's death according to the opinion of the four imams.
Majmoo al-Fataawa, 34/29
For more information please see the answer to question no. 72269
The basic principle is that those who wish to offer condolences should go to the bereaved household to offer condolences, and the bereaved should not go to another house in order to receive condolences.
And Allah knows best.