A more tame version of what I suggested would incorporate Snickers' comment. (Yes, welcome)
You can make your daughter commit to her saying she wants a "birthday" gift and understands
that it is a "birthday" gift. But even if her JW training makes her say, "Nevermind then" you could
send it anyway, allowing her the double-life that her mother won't know about. If she rejects
birthdays, then I would send the gift card or the savings bond as a birthday gift in a birthday card.
If she does not reject the idea of a birthday gift, then maybe I would cave in and send the cash
She is your daughter, and you will never get these years back. If she is tottering on JW or
non-JW, a little push will help.