CA has told me she is going to put me on my husband's bill....

On my husband's credit report was a medical collection for $500.00. We didn't know what it was for, so I called the collection company. It's Northwest Collection. When I called they told me when it was billed, how much the insurance paid and then demanded a credit card. When I said I wanted to look into this the woman told me that she was going to put me on the bill as well and she could do that in the state of Illinois. Then she told me that I shouldn't bother calling back without a credit card. Can she just put me on the bill like that? I can't seem to find anything that says she can't or can.