Allison's jewel previously glowed like this right before she named Vladok.
http://killsixbilliondemons.com/comi...of-names-2-33/
Mottom's forehead jewel spit out white fire the same way right before she turned that insolent guy into a tree AND right before she blasted Gog-Agog's head off.
http://killsixbilliondemons.com/comic/ksbd-4-75/
http://killsixbilliondemons.com/comi...of-names-4-65/
So there are basically (3) possibilities I see:
1) It is a straight up source of abilities/power. So any holder of the key GLORY that Mottom has can use it to turn people into trees (among other things, I'm sure) and explode people's heads.
2) It acts as a power amplifier for already existing abilities. So Mottom can normally blow somebody's head off, but needs the Key to add power/affect somebody like Gog-Agog. Unlikely given Allison doesn't seem to HAVE any magic abilities to amplify.
3) It simply glows like that when its holder uses a certain level of power - it did NOT glow when Mottom blew that other guy into petals. Also unlikely for the same reason as #2, Allison doesn't seem to HAVE any magic abilities at all.