You do need to find out if it is an allergy or something else. Something is affecting her immune system to let the infection happen, or it isn't completely clearing up.
My experience with chronic ear infections is from floppy eared coonhounds, and Hogan had terrible allergies plus chronic ear infections.
Sally has the same goopy ears, so I pulled out the big guns and have her on Zymox. To clear up something, you have to use it every day for about 2 weeks-but Sally gets it every day with maybe only a week or so off. She will actually get excited when she sees the bottle and holds her head still so I can put the stuff in. I have tried a lot of stuff on her, and what works for my greys isn't strong enough for her.
The important part of the instructions...
Do not clean before and during treatment or use any other ear preparations in conjunction (enzyme activity may be disrupted). I do believe you can use the zymox cleaner but the ear stuff cleans as well as treats.
http://www.petkingbrands.com/products/otic.asp
I have both formulas in stock and the ear cleaner to, I just haven't had time to put them up on the site-if you want pricing, shoot me a pm.