While working in nursing, the C. Diff stool I saw was usually yellow.
I'm not a doctor, but based on what I know about Clostridium Difficile Infection, I would ask them to check to see if she has this bacterial infection. People of all ages (including infants and children) can get it and may have green and/or mucous in stools, foul smelling stools, diarrhea, etc. (I had this at age 50 at the same time my mother, 81 at the time, had it....so I have read a lot about it and gone with my mother to multiple doctors. )
New research shows that Prevacid, etc. can upset the natural balance of bacteria in the digestive system and make a person more prone to C. Diff. infection.
Not to frighten you--but C. Diff. can be serious and in some cases, life-threatening. Do not delay--get your daughter in for a stool specimen as soon as possible (like, if there is a reliable clinic you can get to, go there NOW.) Insist she be tested. This is not a well-understood illness and I was lucky, because my Mom had it first and so I knew what the signs and symptoms were. I still had to be a very persistent advocate, to the point of almost being obnoxious, to get the diagnosis and proper treatment.
Meanwhile, your wife should not eliminate dairy altogether---Have her eat yogurt that has "live and active cultures" listed on the label (and eat it 3-6x a day.) The good bacteria helps counter the bad bacteria. Also, check your grocery to see if they carry a drink called kefir. It has good bacteria in it.
The treatment for C. Diff. is antibiotic therapy, and the sooner it is started, the better. Also, do not give her anything like Lomotil/Immodium right now until you know whether she has C. Diff. The diarrhea is nature's way of getting rid of the toxin (that the C.Diff. produces) and you don't want to keep that toxin in the body (which taking Lomotil does) where it can cause harm.
Also, C. Diff. is infectious---Wash hands thoroughly (2X the birthday song) and sanitize anything that gets contaminated with stool with a bleach solution (1 part bleach to 10 parts water)
Please keep us posted as to how things go.
Take care,
Yvette