As Erma was nineteen in the 'Maverick' episode "Red Dog", that would mean she had been in Virginia City four years before.
So let's figure out when that was, and maybe even what show she saw! (Or at least who was in the show....)
Let's start with the timetable from the 'Maverick' point of view......
Beau Maverick had been banished by his Uncle Beauregard, the patriarch of the family, from the United States at the end of the Civil War for bringing shame upon the family. His crime? He had become a hero and won a medal. And even though he did so inadvertantly, it made no never-mind to Pappy.
So Beau went off to England to serve his sentence of five years. The Civil War ended in 1865, so Beau should have returned by 1870. However, I think he ended up staying longer; one reason being that he picked up an English accent while over there. (Beau claimed it was only a slight accent, but it was quite heavy to the American ear. This may be why Erma thought Beau was a stage performer - his diction. Although I think she was more interested in that first syllable, if you know what I mean. Nudge nudge wink wink!) Another reason is the timeline for the entire series. Unlike other shows which are usually set in one location, 'Maverick' traveled all over the Western frontier. That takes time to get from one place to another. Unlike 'Kojak', it's unrealistic to think an episode of 'Maverick' can take place a day later than the last one, or even a week later if that's the way a detective show or medical drama wanted to play it.
So in those three seasons before Beau made his debut, a lot more time passed for Bret and Bart than three years. I think we can still bring in Beau's debut to be in 1871, but I'd be more comfortable if everything was brought forward in time even more.
The same rules of an inner chronology would apply to Beau: For his half of the episodes in the third season, at least a couple of years may have passed and it wouldn't be unreasonable to assume that by the time of his last episode, "Red Dog", it was 1875.
That would mean that Erma Curran saw a theatrical play in Virginia City in 1871 when she was fifteen. And we have just the episode of 'Bonanza' to match to it......
Bonanza: The Iron Butterfly (1971.11.28)
Mariette Hartley .............. Lola
Stefan Gierasch ............... Grady
Allen Garfield ................ Charlie
Jack Collins .................. Mayor
John McCann ................... Bennett
Red Currie .................... Driver
Mills Watson .................. Fontaine
An affair has Hoss risking his life to protect an actress involved in a murder.
There's a general rule of thumb in dating a 'Bonanza' episode - under the sweater but over the bra. No, wait that's Gene Hunt's rule of thumb for dating in general.
The general rule for the 'Bonanza' chronology is that each season represented a year in the Cartwright lives exactly one hundred years previously. So an episode that was broadcast in 1959 took place in Toobworld back in 1859.
"The Iron Butterfly" aired in 1971, so therefore it took place in 1871 and fits in perfectly with the "Red Dog" episode of 'Maverick'. When Erma Curran was in Virginia City, she went to the Piper Opera House where she saw "Romeo And Juliet" starring Miss Lola Fairmont... and an actor whom she would later mistake for Beau Maverick.
Miss Lola Fairmont