Sherbet is a fizzy powder that contains sugar and flavouring as well as an edible acid and base.
The acid may be tartaric, citric or malic acid, and the base may be sodium bicarbonate, sodium carbonate, magnesium carbonate, or a mixture of these and/or other similar carbonates .
Sherbet can be sold by itself or used as a decorative agent on other sweets. The measured qualities of sherbet include granularity, colour, “zing” (acidity) and flavouring (normally a citrus fruit). (source)
So can rabbits eat sherbet?
Unfortunately they can eat it at all.
It is just too sweet for them and full of acid so will hurt them if they eat it.