I think anime to manga is quite rare outside anime film adaptations, care to name a few of those plenty ones you mentioned?
This one is adapted from the light novel however.
Yes, but Char was talking about some series she was watching, not about this series.
Original anime series that got manga adaptation? Sure, those that came to mind easily are those produced by P.A Works: Hanasaku Iroha, Shirobako, Shiroi Suna no Aquatope. Examples that produced by other studios, for instance are Lycoris Recoil and Psycho-Pass
All of those have manga adaptation (and more) during/after their airing, and these are just based on the stuff I remember on top of my head from recent years.
Edit: to add, after checking, Madoka Magica was also an original anime series that became its own franchise with multiple media adaptations including manga format. So plenty to find if we just dig around.
Edit2: Even more mainstream examples would be Pretty Cure and Mobile Suit Gundam. They all originally anime series that spans to however many different media, including plenty of manga adaptations.