All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
If she covered Hajj expenses with an amount equal to her share in her husband`s estate then there is no sin in that. However, if she took more, then it is unlawful for her to do so save with the consent of the rest of the heirs. Moreover, if some of the heirs are minors, then it is unlawful for her to take from their shares because Sharia states that it is unlawful to take and donate the property of the minor. And Allah The Almighty Knows Best.