BRICK WALL #1 - Ancestry of Susanna (1793-1877) - Pennsylvania German

Susanna(h) was born in Pennsylvania, USA in c1793 and was in Ontario by 1812 
when she married (1) Alexandre "Ellick" Larose.  Ellick was a member of the 
Essex County Militia, but later settled in Chinguacousy Twp., Peel County.  He 
may have met Susanna in southern Ontario, or in York/Peel county area.  By 1819 
Ellick was dead and Susanna had married another Frenchman, Pierre LaRoche (Peter 
LaRush).  The remainder of her life was spent in Etobicoke Twp., York County, 
Ontario.

What was Susanna's maiden surname?  She probably emigrated from Pennsylvania 
with her parents and settled in Ontario.  Oral family tradition said she was a 
Mdme. Rousseau - though she was definitely not part of the family of Jean-
Baptiste Rousseau of the Humber.  

She was however a witness at the marriage of William ROUSE to Charlotte 
LONGISWAY.  Perhaps Susanna was a ROUSE?  G.Elmore Reaman in his book "Trail of 
the Black Walnut" states that John ROUSE came from Pennsylvania to Ontario in 
1812 and settled in King Township, York County.  A search in King, revealed 
nothing on John Rouse.  Was Susanna part of his family?

Can anyone break or suggest sources that might break this brick wall??