Who played this blonde at the pool?

Anyone know who this is?
https://www.imdb.com/title/tt0077932/mediaviewer/rm442824961?ref_=ttmi_mi_all_sf_35

I've tried to narrow it down from the cast list by process of elimination, but I'm not sure she's credited even though I think she appears a few more times. She's the one he has tied up to a tree, but kept alive, for some unknown reason.

EDIT: believe it's Kelly Sils, who appears a few more times in the movie. The director referred to her by name in the (very dry) commentary.