I'm a first time ferret parent and although I've been doing quite a lot of research on this, maybe someone could tell me what's wrong.

A few weeks ago I got a female ferret, Athena. She just turned 5 months old. Up until now, she's been very healthy. Just today I noticed that her poop is green and slimy, almost even stringy. She is eating quite well, though, and drinking plenty of water. And the food I buy her has no artificial coloring, and I dont give her tap water, only filtered. She is still active and playful, and isn't acting out of the ordinary. When she's out of her cage, which is quite often, I watch her closely to make sure she doesn't accidentally eat anything, although I had to go out of town for a day and leave her in the care of my brother and friends. However, they didn't say that anything was out of the ordinary.

This is the first time this has happened, should I continue to watch her, see if there are any changes? Should I take her to the vet? Change food? Or give her some ferret lax? Or something else?

Hi.
I think it would be a good idea to get her to a vet.  ECE is relatively common in younger ferrets.  Prolonged diarrhea can lead to fatal dehydration.
 
http://www.peteducation.com/article.cfm?c=11+2071&aid=538
http://www.ferret-universe.com/health/ece.asp

It's best to know what you're dealing with so that you can properly care for her.

THE DOOKS OF HAZARD

Is she the only ferret in the house hold?

I would check around the house to see if she got into anything.  Are you feeding her any treats and if so how much?

Our first ferret Troy (RIP) did this and I was so scared he was my buddy. I took him to the vets thinking omg it is Green Slim Disease. However it was not. He was a rescues and they lady we got him from had been feeding him the same cheap cat food she fed her cats. Her room mate had moved out and just left the sweet baby there and she did not know what to do with him so she called us. We rescue any exotic animals, but Troy was the first ferret. He made us fall in love with them and since we have rescued several more and just plain out went and got a few extra. Best thing is to always take to the vet, when they are ill. Their bodies are so fragile. They can dehydrate in no time and can starve quickly too. They digest their meals within 3 hours and eat about 12 times a day. I'll keep you and your fuzzy in my thoughts and I hope everything goes well.

FerretFuzz