Originally Posted by PatriceJ

hmmmmm ...

she might not have offered to pay because she already knows she should - and will - pay. there might not be an issue here.
the fact that she wants to attend in order to support her friend is not a sure sign that she assumes she can be there gratis. or that she plans to act as an assistant.

your classes are a business operation.
give her two copies of the class schedule, tool & supplies list, fee and payment deadline.
"one for you, the other for your friend."

this is just a thought. can you afford to offer her a small discount on the class fee as a thank-you for bringing a new student into the fold? not something you should feel obligated to do, but it might take away your worry about offending her.