。
She suffered an accident that ended her tennis career.
Literal
She [topic-は] tennis-player [as / for-としては] fatal accident [at-に] encountered.
としては ('as / for X / in the role of X') frames the perspective from which 致命的 ('fatal, decisive') is being judged: the accident might not have been life-ending, but it was career-ending for someone whose work depended on physical performance. 致命的 (chimei-teki) literally 'reaching-life,' carries the literal sense of 'fatal' (as in death) and the figurative sense of 'critical, decisive' — context disambiguates. 事故に遭う ('have/encounter an accident') uses 遭う, the verb for unwanted encounters, distinct from 会う ('meet [a person]'). The に marks what is encountered.