Is it permissible for me to perform Hajj on behalf of my mother without her knowledge, given that she is unable to walk, and then inform her after the completion of the obligation?

Allah has commanded kindness to parents and good companionship with them, as stated in the Almighty's words: (And We have enjoined upon man, to his parents, good treatment) and (And accompany them in [this] world with appropriate kindness). It has been reported in the Hadith that honoring one's parents is among the best deeds after performing prayers on time and before striving in the way of Allah. Therefore, you and your siblings must love your mother and treat her kindly, even if she does not show you care. There is no harm in performing Hajj on behalf of your mother if she is unable to perform it herself, provided you seek her permission for that.