well thats definitely a downer, maybe its inside some of your structure? that happened to me ounce with a butterfly pleco, it stuck inside the cave even after i took the cave out of the water. gl hope you find it alive
BN's are notorious for flat out disappearing and reapering even 6 months later!!! In a DIFFERENT TANK!!
I hope you find her... ALIVE. But I really would leave all the decor in. Also you can drop in a spirulina disc or soemthign after the lights are out.. And the wait ten minutes.. Then turn the lights back on.. But.. I have lost and found numerous BN's and the most amazing one was my friend Bstuvers!! It came up missing in one tank.... And then popped up in another tank that she had a piece of decor from the previous tnak in....