My poor pooch!

Hey everyone! This is my first time posting here, and I need some advice. I have a 8 month old little lady named Tanzy and I've been trying to find a food for her that wont give her super soft poop and accidents in her crate overnight.

We have a 4 year old Chocolate Lab who was on Pro-plan. Naturally we went with proplan for Tanzy as well, but the more research I did I realized it was not the greatest food. I then tried Newman's Own which was not good - she started not being able to hold her stool overnight (which she had previosuly done). Then, we tried Merrick for them both, and I stupidly bought the turducken formula which gave her extremely bad diahhrea/gas and the same problem with the pooping in the crate (the lab has gas from it, and his stools are much softer - but I figured anything would be softer since the proplan made their poop so hard.) By the way, we take her out often and I did expect some problems/issues changing their food. SO now on to Canidae - seemed to make the stool a little bit firmer (still very soft) and then we noticed the mucus in the poop, gave her meds for colitis which ended last week. Well, now she's pooping in her crate again - very very very loose stool.

I gradually changed her food over appx 2-3 week periods. She has been on only Canidae for about 2 weeks. I know I must sound like a moron. I feel awful for "doing" this to her. I just do not know what to do. Give the canidae more time? Try another food? Her coat is okay and she isn't showing signs of being alergic to the food - it's just the poop issue. She also enjoys eating it after she's done it in her crate... I just don't know what to do anymore...