I think I've got enough experience here to at least give you my input. I'm 46, last Friday I just had my 16th sinus surgery. I know I am an unusual case. I'm sure your daughter's sinus issues will not lead to so many surgeries. One surgery has not spawned another and another. I keep getting sinus polyps (have since I was a child). As far as your daughter not having any symptoms, she may be so used to how she feels now that she has no idea how bad it is. This has been the case for me many times. What I feel actually feels normal and I don't notice it or think anything of it. Once I have surgery though it's like someone has taken about 10lbs of weight out of my head and I can breath like I think I never have before. Sinus surgeries used to be fairly rough. The technology and techniques are far more advanced now and surgery (though I still prefer not to have it) is pretty easy. This last one on Friday was by far the easiest. Of course they went in before things got bad, but even the one before that was amazing as far as how I felt after. During the last 2 years I have had 4 of these. One was a pretty big deal because they actually removed bone from the sinus's from eye socket to eye socket. This was done to create a larger opening that would not so easily and often close off. Even with that surgery I went home the same day and actually felt better than I did the day before.
If you have had 2 opinions and they both say it needs to be done, chances are they are giving you good advice. There were a couple surgeries I waited too long on and it created more of a problem than not. If you have further questions, please don't hesitate to ask.
Dave, 46, CF, MRSA, Husband, proud father to a 20 year old Iowa National Guardsman