This is going to come down to a few issues:
1. Does your employer meet the requirements of FMLA, is so your girlfriend has FMLA leave available.
2. Does your girlfriend's condition constitute a disability under State or Federal law? Speak to an employment attorney in your area to determine if this is the case.
3. If the highly contagious condition is the flu, your girlfriend will probably be fired for taking 10 days despite the company's attendance policy.
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Does the employer have 50 employees? And has she worked for the company full time (1250 hours) for at least a year? If so, she may have a right to leave under the Family and Medical Leave Act if her condition qualifies as a "serious health condition" and if it renders her unable to perform the essential functions of her job. The fact that the condition is contagious may or may not make a difference.
You need to contact a local employment lawyer to discuss these issues, plus any other rights that she may have under state or local law. The facts in your question are insufficient to show whether she is protected by the FMLA.