Rupp's earliest TV credits came in the mid-80s, playing saleswomen, waitresses and the like with very small parts on series including "Kate & Allie" (CBS), "Spenser for Hire" (ABC) and "The Days and Nights of Molly Dodd" (NBC). A role in the TV-movie "Mothers, Daughters and Lovers" and a guest turn on "Newhart" came before her 1991 recurring turn on the ABC sitcom "David Rules", Guest appearances on the series "Empty Nest" (NBC), "Evening Shade" (CBS) and "Family Matters" (ABC) kept Rupp in the public eye until she snagged another recurring role, playing Sister Mary Incarnata, the Catholic school teacher of a tennis prodigy, on the ABC sitcom "Phenom" (1993-94). While the series aired, she stayed busy, appearing in the TV-movies "The Odd Couple: Together Again", (CBS) "MacShayne: Winner Takes All" and "MacShayne: Final Roll of the Dice" (both NBC) as well as guest spots on "L.A. Law" (NBC) and "Hearts Afire" (CBS).

When "Phenom" ran out of steam, the practically ubiquitous Rupp didn't disappear but instead continued her TV guest shots, including a memorable role as Jerry's ineffectual manager on a 1995 episode of NBC's "Seinfeld". That same year, she had regular starring roles on two short-lived CBS sitcoms, sticking it out for the six episodes of "The Office" and the five-week run of the romantic comedy "If Not For You". Again, guest work and longforms kept her afloat and in the public's mind until she landed a 1995-96 recurring role on ABC's "The Jeff Foxworthy Show". From 1997-98, Rupp had a memorable recurring role on NBC's hot sitcom "Friends", playing the older woman who Phoebe's odd younger brother Frank Jr. (Giovanni Ribisi) falls for. Together the two overcame resistance from Phoebe (Lisa Kudrow) and the rest of Frank Jr.'s family, follow their hearts and get married. Unfortunately, they were not able to overcome their difficulties conceiving a child until they enlisted the help of Phoebe, who acted as a surrogate and carried the couple's triplets, marking one of the more bizarre ways a sitcom has dealt with an actress' real life pregnancy. This role offered Rupp her greatest visibility to that point, and Alice and the very strange Frank Jr. (approximately twenty years her junior) made an endearing odd couple.

Rupp was featured in the Sally Field directed "The Original Wives Club" installment of HBO's acclaimed "From the Earth to the Moon" before entering American households as Kitty Foreman, hardworking nurse, loving wife of Red (Kurtwood Smith) and somewhat cautious mother of central character Eric (Topher Grace) on "That '70s Show". Rupp's Kitty was a model sitcom mom but not without an edge. Prone to high-pitched pleadings and moments of harried hysteria (handled masterfully by the actress), it was still clear that the devoted, ever-loving and slightly naive Kitty was the one calling the shots in the Foreman family. "That '70s Show" was unique as a sitcom capable of likably rendering both the high school kids and their parents, with both generations winning lots of laughs with well-written dialogue. Kitty's imagined scenes of the horrors that befall Eric when he is out of her sight, an inspired rendering of a mother's worries, and the realistic romance of Kitty and Red proved Rupp's exceptional skills, and she added immeasurably to the strong ensemble.

While her work on television was particularly prolific, Rupp made some notable entries into feature film in addition to her stage credits. In 1988 she debuted with a role in Penny Marshall's acclaimed comedy "Big". Busy on the small screen, she didn't return to features until 1996, when she played the wife of clueless Colonel Hall (Dan Aykroyd) in "Sgt. Bilko". The following year she played one of a group of office workers in the independent comedy "Clockwatchers" (alongside Kudrow) and was also featured in the 1998 comedy "Senseless". In 1999, she lensed a role as the nagging mother of a man (Harland Williams) with romance problems in the independent comedy "X-Girlfriends".