For a HK primary student at lower level, I do not think the teachers will expect they know this word as in a judgment case. Right, may be with a picture to illustrate is better. For me, if this is my son's homework or test, I still will think that the answer should be "Helen was tired." Think in a simple way.
Btw, if "Helen was tried." is about court case, then there is no need to change to "is". So, anyway, if the request is to find a mistake in this sentence, the mistake seems should be the spelling of "tired".