の zaniness

Okay, I know that the particle "no" makes a noun following it into an adjective for the noun in front of it, or makes it a possessive (女友達のあんた, "your girlfriend"). But what does it mean when a conjunction (ie. "と" = "and") is put in there? For example: 女友達とのあんた or 委員長そしての仕事.

none of them make sense. first of all using anta is very rude, instead you should use the persons name when adressing someone thats why jikoshoukai is very important.

の is similar to the english 's or you(r), like Jame's, or Dog's. the sentence   女友達のあんた should be あんたの女友達. But since its rude to adress someone as anta i will just use Ben
ベンの女友達

the と　particle is exactly like the english 'and'.  女友達とのあんた should be ベンと女友達, Ben and girlfriend.

委員長そしての仕事 particles should also never be next to each other. There should always be a subject or object inbetween. If you wanted to say 'Ben and his girlfriend' it should be
'ベンの女友達と'.

Finally the common word for girlfriend is 彼女(Kanojo)