。
She treats me like a baby.
Literal
She [topic-は] me [object-を] [just like-まるで] baby [like-のように] treats.
The simile pattern まるで~のように ('just like X / exactly as if X') is one of Japanese's standard ways of marking a vivid comparison. まるで intensifies the simile — without it, plain のように would still work but with less emphasis. 扱う ('to treat, handle, deal with') is the productive verb for treating someone in a particular way; with this simile pattern it builds the standard 'treats X like Y' construction. 赤ん坊 ('baby, infant') is more vivid than the more general 赤ちゃん, fitting the pointed comparison.