FMLA medical leave and disability issues with employer please help!?

hello, i am having a historectemy in mid august but i've been in a lot of pain lately because of my IUD being lose inside and my uterus is growing over it. My doctor gave me a notice of light duty work. i'm a RNA/CNA so i lift patients all day and the stress down there kills me at night. my employer told me that they cannot accomodate the doctors orders of light duty work. she gave me a sheet for FMLA medical leave. this is unpaid time off, correct? being that she cannot accomodate the work per the doctors orders, i want to apply for disability but my employer refuses to sign the doctors note. according to my disability office, she must sign this note for me to even start the disability process. what can i do?