Occasional mucous in the feces can be normal.  Monitor the litter box closely over the next few days to see if she develops soft stool, diarrhea, or bloody stool.  If the mucous continues or any of these signs start have her examined by a veterinarian. 
A urinary tract infection would not cause mucous in the stool. 
Intestinal parasites, dietary indiscretion, stress, and intestinal bacterial overgrowth are the most common things that cause mucous in the stool along with diarrhea.
Also monitor her thirst, appetite, and energy closely.  If these decrease have her examined.
You could also drop off a fecal sample at your veterinarian to run parasite and bacterial testing.

 This is not necessarily mucus. Now, I know this sounds gross, but if this happens again, take note of the smell of it. ( i know, i know... Lol) If it has a sort of sour smell to it, chances are that your kitty is just releasing the contents of her anal sacs. This is completely normal and naturally happens when a cat (or dog) goes #2. Sometimes it just happens randomly, too. It is a yellowish, sour and stinky liquid. If this is what it is, be glad hers are working properly, because if they do not empty like theyre supposed to, they can become impacted and infected.
 
If it is indeed mucus, however, sometimes this happens when the poops are too firm. I don't know where you live, but I know that during shedding season my cats need a little help just by getting an inch or so long ribbon of hairball gel 2-3 times a week. This can help tremendously.
 
Hope this helps!

 The mucus in eyes, from nose, anus or vagina in cats indicates infection. Your cat might be having urinary tract infection or bladder infection leading to mucus secretion. Take her to Vit to diagnose type of infection which can be bacterial or viral and then get treatment.