All three of my children have had both their tonsils and adenoids taken out. My oldest had her adenoids out at two years old and her tonsils at 4 years old. She snored a lot, had a long history of strep throat and upper respitory problems. She has asthma and allergies like your daugther. My only regret with her was that I didn't push my ENT to do both the first time.
My youngest had both tonsils and adenoids out in February. He is 2 years old. He could not breath if his mouth was closed and had severe sleep apnea. He also drooled all the time. After the surgery, he finally began sleeping the night through and no longer cries in his sleep.
My middle daugther, who is 4 years old, had both out in July. She had speech problems, sleep apnea, mouth breathing and bad breath. Within 24 hours of the surgery, she was speaking beautifully. SHe had never tried to engage anyone in a conversation and now she doesn't stop talking. Our family and friends all amazed at that difference in her. The bad breath has cleared up, she is sleeping soundly during the night and she is no longer a mouth breather.
The complications we ran into were:
1. My oldest daugther did fine with the adenoids and we expected the same with the tonsils. She refused to drink for several days and ended up dehydrating. I blame myself for not giving her the pain medication every 4 hours. I was concerned because it had condeine in it so I waited until she was in pain, this was not a good idea. By the time I realized that this, she was readmitted to the hospital. My son and other daughter got the pain meds every 4 hours around the clock for the first week and then I slowly increased the time between doses.
2. My yonugest son hemorraged 6 days after the surgery. He was readmitted to stop the bleeding. Evidently, he and my middle child both have a blood disorder that we did not know about.
3. My middle daugther developed a fever of 103.5 but that was remedied easily with a change of antibiotics.
My recommendation to you would be to have a neck x-ray of your daugther's adenoids before going to the ENT. My pediatrician ordered it for each of my children because she thought that we would waste the first appointment if we didn't have the films and the ENT wanted them and she was concerned the ENT wouldn't check the adenoids. Sound strange but my sister's ENT did her daugther's tonsils without even looking at the adenoids.
Second, if you are going to have the surgery get a complete family history from both sides. Ask a lot of probing questions. Even if someone was never given a diagnosis but had an on-going problem, you need to know about it. My brother-in-law hemorraged several times after surgeries and dental work but was never tested for the blood disorder my kids have, that information may have made a big difference in what we went through with my son.
Third, if you don't already have an ENT I would recommend making sure he/she is a pediatric doctor and associated with a pediatric hospital. When my son had complications, we called CHOP and told them we were bringing him in. When we walked into the ER, they were ready and knew exactly what to do. My son was ready for surgery before the ENT even examined him. The time saved may have made the difference in him not needing a blood transfusion.
Even with the complications, I think of the procedure as a gift to them. They can all breath without struggling. They can all sleep at night without waking up gasping for breath. They are all happier because they are healthy and well rested.
If you have any questions that I can help you with, please let me know.