Is a girl's Hajj valid despite her performing it at the age of 11, and is her Umrah valid despite her being menstruating and not circumambulating the House?

If the Hajj was performed after puberty, it is considered sufficient as the Hajj of Islam. Doubts about having missed some obligatory acts after completing an act of worship do not affect its validity.

As for Umrah: If the circumambulation (Tawaf) occurred during menstruation, the Umrah is not considered complete according to the majority of scholars. One must refrain from the prohibitions of ihram and return to Mecca to perform the Tawaf and Sa'i. If returning is not possible, then absolution (tahallul) is achieved by sacrificing an animal (hady). If one is unable to do so, then by fasting ten days. That Umrah is not considered valid.

According to the Hanafis, a camel (badana) must be sacrificed in Mecca, and your Umrah is valid. This is because, for them, purity is an obligation whose omission is compensated for by a blood sacrifice. It is permissible to follow this madhhab for ease.