。
Even when she ran into me, she pretended not to know me.
Literal
She [topic-は] me [to-に] met-[even when-ても] feigned-ignorance [object-を] did.
The concessive ~ても ('even if / even though') chained off 会う ('meet') sets up the contrast: 'even though they met,' the expected outcome (acknowledgment) didn't happen. 知らん顔をする — 'to make a not-knowing face,' the classic idiom for feigning ignorance — has a colloquial 知らん in place of 知らない. The combination ~ても + 知らん顔 is a stock structure for describing the silent treatment in casual narrative.