Is it permissible to wear the legal hijab (khimar) with the intention of pleasing Allah, then for oneself, then for the deceased, and does the reward for that reach her?

Your friend, God willing, will be rewarded for her advice to you, and she will receive recompense and reward after her death for your adherence to hijab, based on the Prophet's (peace and blessings be upon him) saying: "Whoever guides to a good deed is like the one who does it," and "When a person dies, all his deeds cease except for three: ongoing charity, knowledge from which others benefit, or a righteous child who supplicates for him." You must hasten to wear the hijab seeking Allah's pleasure and fearing His punishment.