Mine (Lurchers) were on Canagan for ages, but we went through a phase where we had to switch them onto something cheaper. I did a lot of reading and asked a lot of questions and in the end we went for Skinners Field and Trial Salmon. It suited them both really well, healthy skin, coats and poos etc. You can buy it on a monthly subscription from Amazon as well, which brings the cost down even further.
Having tried all the different foods and having them upset her stomach, it might be worth giving her a course of probiotics to get everything back on track before doing anything else. I use Canikur, which is what our vets advise, but buy it online, as it’s much cheaper that way. You could potentially do a week of gentle, home cooked food like white fish and rice, plus the probiotics, before very slowly starting to introduce another food.
When my younger lad was very ill towards the end he could not tolerate anything other than white fish or salmon, with rice or quinoa for weeks. (Tesco do a decent size bag of frozen white fish pretty cheaply and you can just microwave a fillet and add it to rice for a quick meal.) Unfortunately we couldn’t get any weight on him like that, despite him being on 6 feeds a day, so were desperate to find a complete food he could tolerate. Tried Millies, etc, took advice from all the high end food brands about food suitable for dogs with his issues but, ultimately, we found the only food he could tolerate was Chappie, but only the original fish type, the other flavours don’t have the same formula.
Having said all that. If her poos are normal and she’s health in herself, it could be that a course of probiotics might be enough to settle things down and reduce her gaseous emissions.