I'm thinking of videotaping her death to send to her mother
What is the reason for wanting a videotape of her death for her mom?
I just want her mom to have something to remember her by.
Death is a private matter and you recording her death for her mother's peace of mind is still wrong. Respect the sanctity of the death process.
But I feel bad knowing that she was suffering in pain while she died. At least I could lessen her mother's suffering.
Unless the dying person asks you to tape it, please do not. Watching someone die can be traumatic for people. Please don't press the issue.