Floating is not like laying down on a flat surface. There is no pressure on the body, and nothing to push against mom and baby. There are many reasons why normally pregnant women can not lay in certain positions. Pressure can constrict the blood flow to the mother and/or the baby. It can be physically harmful to health of the growing baby.
However, in a sensory deprivation tank she can lay down in any position she wants to!
While I was pregnant it was so comforting to relax on my back. It was euphoric to recline on my belly. No matter how big that baby belly gets, the Epsom salt water gently supports the body and the magic of buoyancy keeps you afloat.
I used to be a stomach sleeper. So I missed this as a full term pregnant woman. Once, while on vacation in Hawaii, (baby moon) my man dug a hole in the sand so I could sunbathe while laying on my belly. It was so loving and wonderful. The sensory deprivation tank was the only other place I felt safe laying on my belly like this.