If I claim my sister as a dependent will I be responsible for any of her bills or mess up her social security or Medicare benefits?

If you claim your sister as a dependent you will not be responsible for her bills.  However, it may affect her Social Security and Medicare benefits.  You will have to contact the Social Security Administration and Medicare to determine the effect it will have on your sister. 

Medicare will not be impacted, nor will regular Social Security or SSDI.
SSI (Supplemental Security Income) or MediCAID could be.

Thank You