Sometimes I give money to my sister, and I like to keep it between me and her, also I like to have it as a secret deed, also as the saying “the right hand gives so the left hand doesn’t know”. However, my mom asks about if I give her money or not? How to hide this and would I lose reward if I don’t?

Ustadh AbdulAziz al-Haqqan

It is not obligatory upon you to say, and you can tell your mother don't worry about it in sha'a Allah or something like that.