Being targeted because of fibormyalgia

I have question a about being targeted at work because of fibromyalgia, I am asking for my girlfriend since she needs to be careful of what she says and does.

She has worked at the same company for close to 7 years and has never had a problem or been written up for anything.

About a year ago my girlfriend was diagnosed with fibromyalgia and was granted FMLA whenever she needs it.

Now she is being written up every couple of months for things that she has been doing since she has been there and now they are against policy or not the way the job needs to be done.

Her co-worker, who does the same job she does and does it the same way she does has not been written up at all.

She has told HR via a letter that she feels she is being targeted and they are doing all this in the hopes that she will quit. They have not even contacted her about it at all.

She is at her wits end with all this and her fibromyalgia has flared up.

What can she do? She goes to work everyday not knowing if she is going to get written up or even possibly fired.

Any and all help is greatly appreciated.

Thank you, Jason