Yuki's getting less-firmer stool after being fed Orijen... & another concern.

likely it is but I would make a call to the vet... orijen is a multiple protein and is abit richer than felidea

If you had simply said that you had done a two week transition to a new food - immediately after which you noticed a loose stool - my suggestion would be to "back up" a little in the transitioning process...say, perhaps 1/4, and continue with that for another week or so and then begin a gradual reduction of the original food - all the time monitoring the stool.

BUT - you've added an interesting complication, the "pink anus"...and, this seems to have happened well after the transition period had been completed.

One of my questions is: how long after you reached the 100% transition point did you notice the loose stool? (you did say she's "on Origen" for two months already...that might indicate that the loose stool started well after the 100% transition point...)

If that's the case and, if it were my cat, I would not suspect the new food as the "culprit".

(Sometimes, if a cat [or human] strains to defecate, part of the intestine will protrude...aka "prolapsed rectum"...often this will resolve itself naturally and, if the cause of the straining is determined and resolved, it will not re-occur. Sometimes a stool softener is required or it might be that constipation is the cause)

However, this requires an answer from you first........