It looks like she's in a breeder box and she might be stressed by it. Stressed fish will hold their fry. I'd try letting her out and then watching her behavior. If she starts hanging out at the bottom of the tank, hiding, avoiding others, nit eating, then I'd try the box again. Or you could provide the fry with plenty of hiding places, let her birth naturally and scoop up the fry when you see them.
Yeah, I had mine in the breeding box when she was pregnant and as Kunsthure said, she is probably stressed (mine was).. I put her back in the tank and she had the babies the next day. Then I scooped them up and put them in the breeding box (the babies)
I've previously decorated my breeder so it was more like a little tank. Had a net one, I put in two thin wide stones for the base, 1 fake plant stalk wedged in there, and a lil piece of javamoss on top. But I had a pretty big net breeder attached to my tank.
I love javamoss for birthing fry. If you're going to move her back to the tank for birthing, if you can get some javamoss in there, attach a clump to the bottom of the tank and let another clump float. Your fry will hide in it until you can schlurp them out. Or you can leave them to fend Fry are sneaky. I've left mine to fend before and months later after thinking they had all been eaten, 10 1cm long babies will suddenly come out of hiding.