5 month old baby will not sleep without the use of Benadryl (diphenhydramine) d. Used a few times to help her breathe at night. Now she won't sleep without it.

Make the call. . No child should "need" drugs to sleep--especially at 5 months old. Take her to the pediatrician asap to check for allergies, apnea, developmental abnormalities.
Taper off. I would not recommend use of Benadryl (diphenhydramine) in a child under age 1..It will generally not help with colds, but it is certainly sedating (the ingredient is sold as a sleep aid). My suggestion is to reduce the dose by 25% each night. Eventually your baby will fall asleep.