Sorry for not specifying. As previously stated, the forie... ?forrie?... "foyer"... entranceway is pretty massive, both Drimmle and the massive man are about 10 meters away. And remember, Marcella sensed a third individual...
The "bomb" can definitely be shut down for a round as it is an electrical device. As per the rules, when an explosive jams (such as the bomb) we would use the Explosive Mishap table on page 137, with 9-10 meaning it goes off as normal. However, both enemies have a bead on the group and if Marcella tries anything, she risks them noticing. Since activating a psychic power requires rolling, I imagine it requires enough effort to show what you are doing, unless you try to "hide it". So if Marcella wants to activate a power without it looking like she is doing so, I will have her make a contested Deceive vs. Perception roll against all enemies who can directly see her.