Is "The cake was bake by her" correct?

Why

Raveena has correctly spotted that passive sentences use a form of "be" ("was", "is", "were") — that half of the pattern is right. The passive voice actually needs TWO pieces working together, the same way the continuous tense needed "am" plus "-ing": a form of "be", AND the main verb changed into its past participle form — "baked", not the plain "bake". "Was bake" leaves the sentence half-built, missing the piece that actually shows the action was done TO the cake rather than something else happening. Test: try other passive sentences the same way — "The letter was write" and "The window was break" both sound just as incomplete as "was bake", while "was written" and "was broken" sound finished, because the past participle is what completes the passive pattern. Her brother is right: passive voice needs "be" plus the past participle together, so it's "was baked", not "was bake".