It requires a prescription in the US, but in Canada it is avail. OTC (lucky Canadians!) There is also a generic version available.
I once got Auralgan from a ped. while my own doctor was out of the office, and for years after I tried to get it again without success. I finally asked why, and here is what I was told. The issue is that unchecked ear infections can progress to something quite serious, and the drops will suppress the symptoms. Peds are afraid to let parents have the drops because they might just treat the pain and not the infection, putting the child's hearing at risk. Peds. are often very stingy about giving out prescriptions for Auralgan.
I've been having chronic ear infections lately, and I'm becoming really resistant to antibiotics. My Dr. has finally allowed me to ride out the infections without antibiotics, but with Auralgan to stop the pain. I'm told not to use it for more than 3 days without taking a break, and if the pain is still present after 3 days, I need to go into the office to make sure there is not something else going on.
Anyway, I recommend you give her a dose of a decongestant containing *Guaifenesin* (Robitussin or the equivalent) about 20 minutes before takeoff, and have her drink from a bottle of water all during takeoff and descent; swallowing will help equalize the pressure. Antihistamines may help her sleep, but they won't do anything to prevent pain; the Guaifenesin is key to clearing the congestion. Of course, all this should be confirmed with your ped., don't just take my word for it.
Good luck!