Well, the problem is, while they are technically not resolved simultaneously, they triggered simultaneously and tried to resolve simultaneously. What this means is, the first Shauna was eliminated "at the same time" her power triggered. And the Comp. Rules say:
702.3 If a triggered power appears or disappears at the same time as the trigger event it’s watching for, it triggers.
The powers are
resolved one at a time, but they are not
activated one at a time. And according to 702.3, removing Shauna after her power triggered won't make it disappear.
Well, while I'd really appreciate Dan's comment, it's already a very good sign Simon agrees with me :P