Help to cast her vote
As Jean finds writing difficult, her support worker could actually mark her X for her. There is a procedure to go through with Jean verifying her identity and a check that her support worker - her companion - can vote in these elections as well. Jean and her support worker go into the polling booth and Jean tells or shows them who she wants to vote for. They might not be able to talk in private, so it might be good for them to talk beforehand. The support worker then marks her X, Jean should check it and then proceed to the ballot box.