Is my fm guppy sick?

My female guppy has been acting a bit strange for the past 29 hours. She is not swimming with the 3 other guppies like usual, and she hovers over the substrate in the corner of the tank. I have been watching the tank like a hawk since I first was suspicious. No one is picking on her. Her fins are clamped and she opens/closes her mouth a lot. Also, she remains vertical most of the time. (tail towards the substrate, head towards the top of the tank). She moves her pectoral fins in a weird way...kind like if two people were paddling a boat out-of-sync and the boat was subsequently rocking to-and-fro. She is pregnant (dark gravid spot) but not hugely pregnant like my other female. She hasn't gotten any fatter/slimmer since the couple weeks I've had her. I haven't seen any baby guppies pop out of her or be in the tank anywhere. Also, she kind of has a dark line running on the underside of her belly from her chin to her tail. It was not there before.

I have a video uploading and I'll post it when it's completed. I love this guppy a lot! Her name is Natasha

Video

Here's a video of her kooky behavior. I hope she's just trying to give birth and isn't deathly ill :cry:

they're nitrite-0 ammonia-0 and nitrate-20 I forgot to mention that. They're what they usually are

*bump* She's not getting any better/any worse. I've kept the tank light off most of the day and fed sparingly.

She's still hanging in there today. She is wedged on some floating plants near the surface and isn't breathing with as much difficulty. Should I quarantine her and maybe add salt for her? I was also thinking about feeding her a bit of pea (incase it's swim bladder)