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If she wore just a little makeup, she'd look even more beautiful.
Literal
She [topic-は] a-little makeup [object-を] does [if-ば] more beautifully would-appear [regret-のに].
The ~ば conditional ('if she did') combined with だろう ('would') and the sentence-final に (contraction of のに, 'and yet, despite that') creates a counterfactual with regret: 'she would look more beautiful if only she wore makeup.' The trailing のに expresses the speaker's disappointment that this potential is unrealized. お化粧 (おけしょう) is the polite form of 化粧.