Skooter
Skooter was introduced in 1965, two years after Charmin Cathy, as the friend of Skipper with whom she shared clothes.
According to Ruth Handler in Dreamdoll:
"Incidentally, we gave Skipper (and her soon-to-be-introduced friend Skooter) their names because cute nicknames were in vogue in the mid-1960, thanks to television shows like 'Gidget', which starred Sally Field"
So Skipper and Skooter were named from those cute nicknames, and seeing the look on Skooter and her looks much alike Charmin Cathy one can deduce that they wanted to give Skooter a personality of a "know it all" girl who annoys the adults compromising them with her constant questions and turns everything upside down. That's how Mattel portrayed her in the commercial.
According with the Urban Dictionary, skooter means "a person that intentionally or unintentionally causes issues which annoy you". Personally I think that the alma mater of Skooter was Charmin' Cathy, presented after the great success of Chatty Cathy, as a tall scholar girl with eyeglasses and an inquisitive glance. She was called "the educated doll" for she could tell 120 phrases and "speak" foreign languages. She would say things like "The Queen lives in Buckingham Palace" and, on a more marketing directed note "Shall we buy a #Barbie doll?" But, apparently Charmin' didn't sell well.
As for Skooter paint we know that the great Martha Armstrong Hand designed it (you will know her better for being the sculptor of Steffie face), gave her freckles and that whimsical side glance where Charmin' Cathy had glass eyes:
"I designed, that is painted, the faces of Midge, Skipper, Tutti and Todd, Francie, and of course my own Rickie as well as Ken's friend Alan and Skipper's friend Skooter" Martha Armstrong-Hand Doll Reader February 1998
What I'd love to know is if the Charmin' Cathy face was the Cathy mold that Mattel charged Martha to sculpt in 1961 and that gained her to work in Mattel first as a face designer and eventually as a sculptor.
Some things will remain a mistery, for now...