What to do now that i have found out that a woman from Cambridgeshire?

[1878]

has said that she has not received an item i sent to her.

I have proof of postage from Royal Mail.
I have looked at her feedback left for others and she has done it to at least 19 other people but Ebay have not got on to her.
She is blatantly scamming ordinary people.
I sent the item first class but not signed for (Big Mistake)
I would like to contact ebay but then she will leave me bad feedback if she finds out.
Should i make her life a complete misery over £20 or just let it go and let her carry on robbing people?
I have her home address and have even been on her Facebook page, just waiting to see if she slips up.
I have had to refund the £20 and i know she got the item.