I have been in your daughter's shoes before and I know how suffering and what she feels. It was all over my body when I work up one morning... and I had to head of to school that day! Trying to cover it up was so hard...
I went to see my family doctor but it didn't clear... one day, another of a doctor I see referred me to a skin specialist where I finally got to know the name of my condition. It's chronic idiopathic urticaria. It took many years till it started to clear... but then I found out I also had cold urticaria. But my condition is much better than before.
There can be many factors causing her to get hives. Do you remember the first breakout? When was it? What was she doing? Where is she? Sometimes this info can help you to discover a cause as time goes by.
Does she have any swellings? Swollen lips, eyelids, face? If she can't sleep at night, maybe benadryl might help. Take it about 30 mins before she goes to bed or so... hyrodxzine(cant remeber the spelling) will help as I find it really drowsy when I took it before. Something you have to take note is... never give her warm/hot water to bathe in... it causes the hives to be worse. Use cold water if possible
but not freezing cold.
If the hives lasts for more than 6 weeks continously... it could be a chronic form of urticaria. But will have to be diagnosed by a dermatologist to confirm. What doctor is she seeing currently?
Usually for chronic hives, creams like hydrocortisone don't work well on us. I've used them and rather than helping with the itch, they tend to thin the skin and cause easy tearing. But you can look for cromolyn cream which many with chronic hives find it helpful. How old is your daughter?
Feel free to ask me if you need help... hope your daughter will have better relieve from the nasty hives! Good luck!