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If you see her pooping, it's pregnancy. However, are you sure its a female? The one fin that tells you is not clearly visible and in your pics, looks like a male's gonopodium.
Great, I see poop and an extended Anal fin. So it's definitely a female and she is preggers. No telling however how long till she gives birth so be prepared with a net breeder or other breeder trap or having a lot of plants ( real or fake) in the tank for the fry to hide in.