Drop the attitude, take whats on board in the warnings in a positive way, ask her boss to detail to her how she could improve her performance ask that she be given time and maybe even training so that she can keep her job, have her explain to her boss that she really needs this job.
If she doesn't want to do the above, she deserves the third warning, in business your staff are your business, understand that, he needs someone in that position who wants the job, doesn't sound like she does, communicating isnt kissing ass and a job is a privilege especially in today economic climate, not a given.