Kneedeep. At 7 your daughter would qualify for the enuresis (bedwetting) clinic via your gp. They will discuss strategies with you and come up with an action plan. If that doesn't work they can either loan you an alarm or in some cases if necessary they can offer medication.
I feel your pain as my ds1 is currently wetting the bed since going back onto gluten for his coeliac test. Apparently its to do with the inflammation in his bowel putting pressure on his bladder. Fortunately for us, if we wake him to go to the toilet at about 11.00 he is usually dry for the rest of the night.
Best thing we found was to buy several of the soft hippychick bed protector sheets and get him to lie on one of those instead of a normal sheet. Then if/when he does have an accident we can just take off the wet one, and replace it with another. They aren't cheap, but are worth every penny imho.
Mind you, my situation isn't helped by my poor little old lady dog (who is very ill) developing night incontinence now as well. I often have both human and dog bedding to wash before I can even start the day. Its very wearing and as you say, when you are tired from them waking you in the night and you are faced with yet another load of wet bedding, its difficult not to get frustrated sometimes.
In my case I know it will stop again almost as soon as he comes back off gluten.
I hope you manage to sort something out for your dd soon.