Foods for anal gland problems

Hello.

I have a very healthy half pug/ quarter Chihuahua/quarter jack Russell female who is 4 & a half. She has been suffering from Anal gland issues and I have taken her to the vet twice and they have been infected so she has had 2 courses on antibiotics and her glands have been expressed once. I don't want to keep having her glands expressed as I don't want them to be damaged but I can't seem to get rid of the problem and the smell. She is constantly licking her bum and doing that awful sucking sound, and the occasional scooting. I want to change her diet to something with high fibre. Does anyone have any suggestions/had similar problems and are there any foods you can suggest? I was told to put crumbled wheatabix on top of her dinner for the fibre content but have read online to avoid any commercial food with any type of grain in it. I usually feed a mix of wet and dry.

I would really appreciate any suggestions as I really want to get to the bottom of this without having her glands expressed.

Thanks,