adult dog messing in cage

Question
My husband and I have a puggle who is just over a year old.  Recently, she has begun pooping in her crate overnight.  The first couple of times it happened, she had diarrhea.  We cleaned her crate, took her outside to eliminate further and continued to keep the routine normal, making sure not to baby her or give her extra attention.  However, recently, she has been having solid BMs almost every night in her crate.  She is entirely house-trained.  She rings a bell on the door to let us know when she has to go.  She does not go in her crate when left during the day.  We take her out everynight around 10pm to make sure that she has gone before we put her in her crate.
In addition, she shares a crate with our other dog - a Cavachon, also just over a year old.  We are concerned about the affects it might be having on her as well.  
Any information on why she may be doing this and what we can do to help her would be very much appreciated!
Thanks,
Amy

Answer
Amy,
The first think I would try is getting a separate crate for each dog.  She seems to be at the age where she is maturing and she could be doing this as a means of "marking" her space.     With everything else you have said about her, it doesn't seem like she can't hold it.   
If that doesn't work, we'll go to step 2, however, I feel pretty sure it will help if they each have their own personal space.