Ruby is one of the patients at Blofeld's allergy clinic at Piz Gloria, Switzerland.
How she and Bond meet:
Disguised as Sir Hillary Bray, Bond meets Ruby at Blofeld's clinic and then sleeps with her to find out Blofeld's plans (imagine that).
How she helps save the day:
As Bond is in Ruby's room, she undergoes Blofeld's mind conditioning treatment. When Bond witnesses this process, he has a better understanding of how Blofeld plans to distribute Virus Omega to the world. While staying with Ruby, Bond learns the real names of all the patients and alerts the proper authorities.
Trivia:
In the novel, her name is Ruby Windsor.
Though one of several Bond girls to appear in both an official Bond movie and the 1967 Bond satire Casino Royale, Angela Scoular has the unique distinction of having a nude scene with Bond in both her movies! Her role in On Her Majesty's Secret Service has Ruby laying naked on a bed while being seduced by Bond George Lazenby. While in Casino Royale, she plays Buttercup, one of M's many daughters who ends up bathing with "official James Bond" David Niven.