Green’s Dictionary of Slang

susy n.¹

also suzie

[rhy. sl. Susy Anna = tanner n.]

sixpence.

1934		P. Allingham Cheapjack 167: ‘Suzie,’ like ‘sprasey,’ is the slang for sixpence.
2001		J. Burkardt ‘Rhyming Sl.’ Wordplay 🌐 Susy Susy Anna a tanner a sixpence.