If Olive's Magical Reputation is her highest reputation at 14 years of age and it's above 100, after attending a class Olive runs into Wendy who encourages her to participate in the Combat Tournament and to fight her there. She also works part time in the Pawn Shop and possibly attends Magical Class as an assistant.
These are approximate ranges for the old beta version. Wendy is a lot more powerful in the Steam version and is highly skilled in Melee as well as magical combat. Keep in mind that Wendy's melee and magical attack and defense raise with age too, as does her combat and magical skill. Since they are not shown during the Combat Tournament it's hard to find out what they are. If Olive has a birthday on October, she faces a Wendy 1 year older than her, who is tougher to fight.
StrategyWendy is the weaker of the two fighter rivals, preferring to specialize in hitting hard with magical attacks rather than have high HP and sustain a lot of punishment. This means that she's easy to fight as long as you have good Magical skill. Even if Olive ignores raising her magical skills and focuses heavily on combat skills instead later, Wendy isn't too hard. As long as Olive has a decent Constitution, she can tank a few spells while hitting her for good damage. Raising Magical Defense a bit also helps.