She may very well be sick. Or, she may be fine. Unless you take a stool sample to a vet for analysis, you are just guessing. Are you absolutely positive that the white foamy "slime" is stool? Did you observe her leaving it? Or, are you just surmising that's what it is? Are there any white or yellowish chalky solids with it (uric matter)? Could it be regurgitated stomach contents? What does it smell like? Has she exhibited any other symptoms, such as mouth breathing? Any neurological symptoms like head-waving or "star-gazing". Is she still taking water? How does she act when you pick her up or handle her? Is she crawling through your hands actively trying to get away (as they normally do) or is she just limp and listless? Are you, because of your concern, handling her too much and stressing her?
If the loss of appetite and abnormal stool are the only symptoms, then that would be indicative of a parasitic infection of the intestinal tract and you are probably safe just scooping the fecal matter into a clean medicine bottle or 35mm film canister and taking it to a vet for analysis. When you do, ask him/her for 2 or 3 Fecalyzer collection kits to make future collection easier. If there are any other symptoms, or you don't know, then you need to take the snake to a good herp vet and have her checked out. Most of the things that affect colubrid snakes are easily treatable if detected early, such as pinworms, roundworms, hookworms, giardia, entamoeba, pseudomonas, coccidia, etc. The real killer is cryptosporidium. If that is detected, then that animal will likely need to be destroyed along with all of it's cage furnishings and probably the cage itself, and it MUST be isolated from the rest of your collection immediately. There has been VERY limited success with treating crypto with sulfa-based drugs, probably in the 1% range. The risk to the rest of the collection isn't worth the extremely low probability of curing the animal without infecting the other animals. It is easily vectored from one cage to another by the keeper (as are many other pathogens), particularly if he doesn't disinfect his hands between cages, or puts the animals in holding cages while cleaning and doesn't disinfect the holding cage between animals. Luckily, it is relatively rare at this point, and seems to affect boids and certain viperids or crotalids more often than colubrids and elapids. Another killer is Inclusion Body Disease, which also affects mainly boids, but I'm sure it can probably be transmitted to other families.
