Non-usable fin?

[Fishy_Friends]

One of my female fancy guppies has become unable to move her pectoral fin. It sticks straight out and looks very frayed. Other than that she looks to be in great condition.
Tank size- 29 gallons
Ammonia- 0
Nitrate- 20
Nitrite- 0
pH- 7.1
Anyone seen this before?

 

[GoldfishGuy]

Tank mates?

 

[Fishy_Friends]

Other guppies and Albino Corys. She lost it in the other fin too

 

[Fishy_Friends]

Still has full use of everything else?