She shouldn't be doing anything unofficial and if she does go into a job share agreement then it should be down in writing. Otherwise, chances are, something is going to come back to bite.
She also needs to check what the impact on PRSI contributions will be. I've had cases in the past where to ensure PRSI contributions were maximised, both job sharers had to work one week at the start of a year (I think it has to do with when Jan 1st falls).
In theory though, she is halving her salary and pension contributions.