What is [incumbent] upon a sister who intended Umrah from the miqat, then menstruated and forgot to say the supplication, "If a barrier prevents me, then my place is where I am held," and wore the niqab, and after she became pure, she circumambulated the House out of ignorance while she was menstruating, then returned to Riyadh?

First: A menstruating woman's ihram is valid, but she should not perform tawaf until she becomes pure. If your sister entered ihram and then menstruated, she must complete her Umrah after her purification. If she traveled before performing tawaf, she must return and complete her Umrah.

Second: A woman in ihram is prohibited from wearing the niqab. She should cover her face in the presence of non-mahram men by lowering a covering over it. Your sister's wearing of the niqab can be interpreted in two ways: 1. She intended to reject her ihram. This does not invalidate the ihram, as it can only be rejected for a legitimate shar'i reason, such as being prevented (ihsar). The woman remains in her state of ihram, and her Umrah is valid. She must repent, and expiation (fidyah) is required if she knowingly and rememberingly committed a prohibition. 2. She wore the niqab without intending to nullify her Umrah. This is a commission of a prohibited act. However, if she was ignorant (unaware of the prohibition), there is nothing upon her.

In summary: If your sister performed tawaf after her purification, her tawaf is valid, and her intention to nullify the Umrah or her wearing of the niqab does not harm it. If she performed sa'i and shortened her hair, her Umrah is complete. If she was ignorant regarding wearing the niqab, there is nothing upon her.