If you think Marvel and DC are rebooting their characters (and continuities) more frequently than ever...
This particular story is from the early Silver Age "romance comic" phase of her career.
This never-reprinted story from Modeling with Millie #54 (1967); written by Gary Friedrich, penciled by Odgen Whitney, and inked (uncredited) by Frank Giacoia; was Millie the Marvel's only appearance.
It was also the final issue of this particular title.
Over at her ongoing "sister" title, Millie the Model, the character returned to her previous Archie Comics-influenced format, once more becoming a teen-humor title without ongoing storylines.
Trivia: From 1945 to 1973, there was always at least one Millie title from Atlas/Marvel, for a total of five different series, plus annuals, a couple of one-shots, an ongoing strip in Comedy Comics, and a spin-off series for her rival, Chili!
Her main title ran for 207 issues, and was, until Fantastic Four #207 came out in 1979, Marvel's longest-running character-named book!
(Books with longer runs like Mighty Thor, Incredible Hulk, and Captain America had different names [Journey into Mystery, Tales to Astonish, and Tales of Suspense, respectively] before becoming "character" titles.
Millie's flagship title was always Millie the Model!)
Millie was rebooted several times going from a romance/humor hybrid to Archie-style humor to romance/soap opera and finally back to Archie-style humor with changes to the characters' ages, professions, and relationships at each stage.
Millie Collins, despite being shown as outside the Marvel Universe in this tale, has appeared as part of the mainstream Marvel universe in several titles, including the "Wedding of Reed and Sue" in Fantastic Four Annual #3 (and Marvels #2), Dazzler #34, Sensational She-Hulk #60, and the Models, Inc mini-series.
In the 1980s, a middle-aged Millie appeared in the Star Comics mini-series Misty, about the teen-age daughter of Millie's brother!
(The best thing about this Trina Robbins-produced mini-series was the retro look and use of readers' designs for the characters' clothes.)
Millie was scheduled to be rebooted in 2003 as a teen-age tennis player in a manga-style mini-series called 15-Love.
When the project was finally published in 2011 (yeah, eight years later), the lead character was Millie's teen-age niece (though Millie herself did appear briefly)!
