What's the meaning of "she is a real pip"?
It's originally American English.
- colloquial (originally and chiefly U.S.). Something remarkably good; an excellent or very attractive person or thing.
(Oxford English Dictionary)
informal An excellent or very attractive person or thing.
(Oxford)
Slang, Obsolete
a person or thing much admired
(Webster’s New World College Dictionary, 4th Edition. Copyright © 2010), quoted at Collins)
In the show, it could have been used sarcastically, like any other positive descriptor.
Jonathon Green, Chambers Dictionary of Slang (2008) offers a series of meanings for pip as U.S. slang, and conveniently includes approximate dates of first known occurrence for each meaning:
pip n. {abbr[eviation of] PIPPIN n. ["|mid-17C+| (also pipkin, pippins) a term of approval or congratulation, applied to a person; thus affectionate term of address my pippin"]} 1 |late 19C+| (orig. US) the very best, the finest example. 2 |1900s| (US) a negative, bad example. 3 |1920s–30s| (US) an innocent. 4 |1950s| an attractive woman.
The example that the poster asks about clearly uses pip in the sense of Green's definition 4.
Early instances of 'pip' used in the relevant sense
Although Green states that pip in the relevant sense originated as US slang, he also says that its lineage goes back to the 1600s (and presumably to Great Britain), as pippin.
Green seems to have misgauged the earliest instance of pip in the specific sense of "an attractive woman" by several decades. From Rex Beach, The Barrier, serialized in the Santa Cruz [California] Evening News (March 16, 1909):
"Those your kids, too, eh?" Stark continued.
"Yes, and I got another one besides—older, a girl." "She's a 'pip,' too," said "No Creek" Lee fervently. "She's plumb beautiful."
From "'Dealin' Out Jobs' Is Organization's Business, Says Ward Heeler in 'The Crack in the Bell'," in the Philadelphia [Pennsylvania] Ledger (May 13, 1918):
"I very much hope that I may meet you again," he declared with fervor, eyes still clinging to the figure of the girl.
"Oh, I hope so," echoed Sylvy, sincerely enough, though not very confidently.
"Ain't she a pip?" demanded Kelly, advancing from the background in which he had temporarily obscured himself.
From "Loud and Clear: Karl Nakagawa," in the [San Francisco, California] Shin Sekai (June 5, 1931):
Like all good boys, he has his weakness. Looks like an interracial romance is in bloom. The writer met his weakness recently and she's a pip. One would wonder how such a lovely creature could ever forsake men of her own race. Her form, her pearly white skin, her eyes—what an example of beauty! Makes one's heart go pitter-pat.
And in an episode of the nationally serialized daily newspaper comic strip Alley Oop in the Borger [Texas] Daily Herald (September 4, 1938) a character named Foozy says this:
Say—who's th' doll with Oola there? She's a pip! My gosh, what gorgeous hair!
Not surprisingly, there are instances from the same period in which speakers use longer forms of pip with the same evident meaning. From Stuart Stone, "Matched by Mail," in the Tacoma [Washington] Times (September 3, 1910):
"Oh, Tex—she'll do. She's a pippinoola—that Miss Nellie. Take me in and introduce me as her true lovin' heart."
From Joseph Kescel, "The Mirage," in the El Paso Times (April 6, 1917):
"Who was that I saw you with a few moments ago?" asked the "Mirage."
"The young lady I wrote to you about, staying over at the Thompsons'. She's the best that has come this way in a long time. Sure, you're going to meet her. You'll have to speak loudly to her—hearing's not very good. Too bad too for she's a pippin."
It bears noting in connection with pippin that the word has been applied to "a crisp tart apple having usu. yellow or greenish-yellow skin strongly flushed with red and used esp. for cooking" since the fifteenth century, according to Merriam-Webster's Eleventh Collegiate Dictionary (2003). The Eleventh Collegiate considers the later meaning of pippin—"a highly admired or or very admirable person or thing"—to have emerged from the original apple meaning.