。
She couldn't even stand the sight of him.
Literal
She [topic-は] him [object-を] saw [just-だけ] [even-でも] unpleasant was.
見ただけでも is a layered concessive: 見た ('saw') + だけ ('just, only') + でも ('even') = 'even just having seen.' The construction pivots on the contrast between the minimal action (just looking, no further interaction) and the strong reaction (いやだった, 'was unpleasant') — emphasizing how strong the aversion is. いや here is a na-adjective meaning 'unpleasant, distasteful' — a softer word than 嫌い ('hate'), describing a feeling of distaste rather than active hatred.