The script changed a lot in various drafts. Here are two version of this action. The probe uses a "SMALL WHIPLASH ENERGY BOLT" in both. It grabs Ilia with a "tendril", like when it is gathering data from the consoles.
The first is redshirt death is in a script dated July 19, 1978. In this one
both guards get zapped just for drawing their phasers.
View attachment 30125
In this revised page from late September 27 where
one guard fires at the probe and gets zapped...
View attachment 30126
...my guess is it's this second one that was filmed because in the footage the one guy clearly aims his phaser at the probe.