why does she lie? I have no idea, and the thought that I, or anyone else, would be able to answer that question is silly. But the question still remains...does her lying about her size impact your ability to do your job? If she is lying about work issues, bring it to your boss. If she isn't carrying her share of the workload, bring it to your boss. Everything else is non-work related and just really doesn't matter. Move forward, move on...
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Providing alternative truths since the invention of time