Kelly was there when they originally talked to
the Mallers in the lobby (well up in the guard room).
Burt says that they heard everything. If you remember
Michael had just been having a go at Kelly about falling asleep while on guard duty and maybe Kelly thought she'd be better off with them in
the tower. Then when she realised what was going on she regretted it. It would explain why she was so upset about
Tommy's death. It wouldn't have happened if they hadn't had to call the Zombies to chase off the mallers. Its probably the same reason she takes fault for
Saul's injury. This was right when Kelly started to change her attitude towards everyone. I think she got in touch with the mallers and told them what was happening in the tower, hoping that they would come in and change the leadership situation. There was probably some sort of deal that would have lead to protection for her, or at least she thought so.