。
My mother made me who I am today.
Literal
Mother [topic-は] me [object-を] today [possessive-の] me [into-に] did-[benefactive-てくれた]
私を今日の私にしてくれた = 'made me into today's me (for my benefit).' ~にする = 'to make (something) into X.' The doubling of 私 — object and goal — creates a compact, powerful expression of gratitude.