You need to find out if it's a physical issue with her facial structure or an allergic issue from a food or germs. And yes it may be a combination. Out of my 5 kids, the two blondes had the severe problems. They were alike medically but boy/girl. Looke dlike their dad... who I found out also had bad ear/throat problems. Doc said it was facial structure where the Eustacian tube was placed during youth. You can't change that!
Then you have the allergy thing. DD was tested by allergist. No allergies, but still the sinus, swelling/ear clogging etc etc. ending up with asthma. They now call it Reactive Airways Disease. In plain English: you start to get a cold, sinuses start dripping a wee bit, most of us deal with it and go on,blowing nose etc. Child with RAD drips post nasal slightly down throat and it irritates lungs. Even a minor bit causes asthmatic cough. Solution? Treat the most minor sniffle with decongestants. Keep them up even after the drippy nose stops. You want to not only stop the srip, you want to stop inflammation in the eustation tube and let it drain. That draining may take days/weeks.
Clues: if DD complains her ear is stuffy-- sounds are muffled-- her ear *pops* and *crackles* , give decongestant. If within 20 minutes she says ears *clear* or begin to *pop*, keep her on decongestant for days or at least a week. Mine were on it a month at a time. Teach them to recognize the symptoms early. Treat early before it gets full blown.
Both mine ended up with tonsilectomies ages 4-6 and that cleared them up. DD who never had problems with this ended up with tonsilectomy & sinus surgery in her 20s. Who'd knew? Again, facial structure has a lot to do with it. As adults, the two girls look like twins.
One warning: was told that hearing was very important in the 12-18 month range for developmental reasons. Make sure child is being treated if there is ear problems during that period.
And lastly, sometimes no matter what you do...

DS had first ear infection at 3 weeks, tubes 3 times and ruptured eardrum for 2 years. Tonsilectomy at 4 1/2. He's fine as an adult. He has selective hearing-- if you know what i mean!
Ear problems are a very frustrating, continuing problem for some children. You just do what you can and use the best doctors you can, but I truly believe in bad cases that continuous decongestant use helps prevent worse cases. Find the one that works for your child. They don't all work the same. Read labels. Read reports. Discuss with doctors and know your own child.
Also, for about $50 you can buy an otoscope and monitor your child's ears. Bought my DD one for her kids about 5 years ago. She took it to her pediatrician, who showed her what to look for. Worked well for her!