Singing water bones... this is a very weird dream. Toby doesn't want to get any closer than she already is. She's too dense to swim, and if it's deep enough for a merrow the bottom might drop off too steeply for her to just climb back out. Also the whole 'attacked by a blight-dream' thing.

"See if your friend there will grab it so you can pull them out," she says patiently, long used to clarifying for her people. Normally merrows out on the land are weakened and can't make this kind of noise to any effect. Maybe this doesn't apply to blight dreams, but look, she has to try and maintain casualty.