To figure out her ethics and weather or not it's cannibalism we need to figure out some things first.
1: what is her body made of?
In a previous chapter we see her grow root on her ass that stuck her to the ground, so we can infer that she has a root system as part of her body, but is she basically a human who has plants growing inside of her or is her body made of plant?
2: Does she consider the sprout as "part of her body"?
We see the sprout grow on her head and at her will it can grow meaning she has power over it, but does she, and by extension her species, consider the sprouts to actively be a part of their "body" or selves, or is the sprout considered just something that grows on them and they happen to have an influence on it?