、。
She's in a bad mood — and that's because she always misses the subway and ends up walking to work.
Literal
She [topic-は] mood [subject-が] is-bad [reason-というのも], always subway [to-に] misses-train workplace [until-まで] walk [predicament-羽目] became [because-からだ].
A long, layered single sentence with two notable patterns. ~というのも ('the reason being that, that's because') is a structuring device that flags an upcoming explanation, often used in writing or measured speech. ~羽目になる ('to end up in a (bad) situation') is a fixed idiom for involuntary, regrettable outcomes — the 羽目 ('predicament, scrape') comes from horse-tack vocabulary, where 羽目を外す ('to remove a horse's bridle, to break loose') gave the modern figurative 'to lose control, to go wild.' 乗り遅れる is itself a compound (乗る 'board' + 遅れる 'be late') for missing transit. The whole sentence is a small character portrait — chronic lateness causing chronic frustration.