Btw, “douki” isn't her name... 同期 / dōki / douki means that MC and FMC started at the company the same year. The author changed the name from "Senpai is Mine" to "Ganbare, Douki-chan" probably to correct the misconception that FMC is a kouhai and also to make it clear who we could (should?) be cheering for. We may want to update the MangaDex page with the official title for this manga (and not as an alternate name) because otherwise it's misleading... (Or unless you want beauty mark-chan to win, haha...)
If you do want to check, throughout the manga MC and FMC have called each other "co-worker". Also in chapter seven, beauty mark kouhai calls douki-chan her "senpai".