1960 Private Property - Very beautiful Kate Manx
https://www.imdb.com/name/nm0544347/
Two bad guys stalk a woman at a secluded property.
-First they spy on her swimming nude (from a distance so not much seen)
-In the climax one guy has killed the other and is chasing Kate around the house. She climbs into the pool to hide with a brilliant underwater shot of her dress flying up to show off her panties (Many Wetlook fans are born).
-Her husband comes to save her and as she climbs out of the pool her dress has completely fallen to reveal her wet dress and panties (oversized but sexy)