Suing For Child Support And Medical Bills

My husband's ex wife is threatening to sue me for child support and half of their son's medical bills. can she do this to me? my husband is without a job right now but has applied for social security benefits. I just need to know my rights so i can protect myself. Does she have the right to come after me since my husband is without a job right now? I know in their divorce agreement he is suppose to pay half of their child's medical bills. We have been married for almost 3 years and they have been divorced for 12 years.