Even if it's someone else who makes her happy, as long as she's happy, that's fine.
Literal
Other someone [subject-が] her [object-を] happy [to-に] made [even-if-としても], she [subject-が] happy [if-なら], that [with-で] good.
Two stacked conditionals plus a conclusion. ~としても = 'even supposing that ~, even if ~' (concessive hypothetical). なら is a topic-conditional 'if it's the case that ~.' 幸せにする is the set causative-like idiom 'to make (someone) happy.' それで良い is a fixed phrase 'that's good enough, that's fine' — the で here is the instrumental 'with that,' not the copula.