
From a quick glance, one of the common ingredients in the complete foods listed is rice. It could be that your girl is intolerant of or allergic to this grain or several. Food intolerances are the most common reasons for collitis type symptoms becoming chronic, however there is a possibility of an underlying medical cause for collitis symptoms which will hopefully be discovered or ruled out by the test results you are waiting for or additional bloods.
Personally I would feed a home prepared diet, excluding anything ingredient wise you've previously fed - perhaps using thoroughly cooked and mashed potato (no added salt or dairy) as a filler. For protein you could perhaps try turkey, lamb, rabbit or white fish. If you decide to go down this route, along with the potato select one and one only meat/game/fish protein and dont be tempted to add *anything* else by way of treats, left overs etc. Stop any current food immediately - anything which is currently being fed and making her unwell does not need to be gradually changed over from but IME abandoned immediately. Rest her system for 24 hours and introduce a small amount of the new home diet increasing the quantitity VERY gradually over two or three days. All being well her insides will have time to soothe and heal over and this in itself should ease her symptoms. If she remains OK on your chosen regime, stick with it religiously until such times as test results or your vet dictate otherwise.
Other food types to be avoided in the meantime are any dairy products :)
HTH, please update on your girl's progress and any diagnosis made.
best wishes, Teri