Many people find happiness and a great deal of comfort in religion. I'm not a JW, but I have my own religious beliefs and can see where your daughter is coming from. You should understand that there are many who find in religion a purpose for existing. Some may be comfortable in not knowing, but I can tell you that destroying someone's religious beliefs will not endear you to them, but may instead cause deep seated resentment and depression in the form of cognitive dissonance.
If your daughter is happy in her beliefs, I recommend you respect her wishes and not seek to undermine them unless those beliefs are being used by others to alienate her from family or friends. When people use the religious beliefs of others as a means of control, that can be challenged without destroying a person's core beliefs. But that's another problem entirely.