Female Guppy Looking Weird

Today when I got home I noticed one of my female guppies hanging around almost on the gravel and hidden by my two fake plants and one real plant. I thought she could be in labour but two hours later with her still in the same place made me doubt it as there are no fry.
 
Her stomach looks squared off, but not exactly in healthy "pregnant" way. There is also a fairly large opening just below her gravid spot. Her tail also looks a bit odd. Any ideas what it could be? I was planning on doing a 50-70% water change today just because I'm going to be gone for three days. 
 
Thanks in advance!
 

 
 
Edit: I forgot to mention that she is in a 20 gallon tank with five other guppies, three zebra danios and three male endlers. The water is 79 degrees Fahrenheit. 

I don't see anything wrong physically, any new fish or decorations?

No new additions. I did have a fish die yesterday, perfectly healthy looked to be about 5-6 months old compared to my 4 month fry. I did a water change and everyone else is eating and being active, even two of the heavily pregnant females. She isn't coming up to eat and sluggishly swims around the plants or hides. 

Could you tell me what the water parameters are like? This can help identify the problem.
Tank size?
Tank mates?
Thanks.

AshleyNZ said:

Could you tell me what the water parameters are like? This can help identify the problem.
Tank size?
Tank mates?
Thanks.

Click to expand...

I added that to the the first post. But it's a 20 gallon with the temperature set at 79 degrees. In the tank there are three zebra danios, three male endlers and 5 guppies total including her. There is also a mystery snail. As of today, there is a small red prick on her stomach, vertical to her eye. it looks like she could have been scratched by something.
 
Unfortunately I am leaving in a few minutes out of state and won't be back until monday. I did a 70% water change last night but I don't know what to do about her. 

Oops, sorry. I think that tank is too small for the zebra danios, as they are highly active, and should be kept in a group of 6+. Groups less than that can cause aggression (Been there myself) 

That temperature is also WAY high. What temperature should the Danios be kept at?