A short bio  (picture) of the Countess is available at
 
http://www.fortunecity.com/victorian/riley/787/Napoleon/France/Biografies/Walewska.html
 
I do not find anything that supports a possible connection with "The Van Sisters"' Mary Valevsky. BTW, the variant spellings merely reflect different systems of transliteration from the Polish spelling into French Russian, & English.