On first glance, the search for electronic devices and drives is a bit of a puzzler. Usually you think of computer evidence being central when someone has illicit photos/videos, or maybe if there are financial records that point to their crimes. Neither of those seem to apply here. I'm sure the authorities would love to find an incriminating email or a google search, but this just doesn't seem to be a case that would turn on that kind of evidence.
Instead, I think what would matter would be being able to prove that the lunch was poisoned, the testimony of Ian, Simon and others, as well as her own statements and actions that could be used against her.
My initial thought was that the search for electronic evidence was just a sort of cherry on top where the police hoped they could find something incriminating. However, in EP's court appearance, the prosecutor said they would need weeks to go through all the electronic evidence, so maybe there is something specific they want to find.
Also, if there really is damaging evidence stored on electronic devices, why didn't EP just destroy it? A few minutes with a drill or handsaw could have done a lot of damage and made it virtually impossible to retrieve any data.