。
She's having second thoughts about buying another car.
Literal
[topic-は] another 1-counter car [object-を] buy thing [object-を] is-reconsidering.
考え直す is a compound verb: 考える ('think, consider') + 直す ('redo, fix') — together 'rethink, reconsider.' The auxiliary ~直す universally means 'do over,' attaching to many verbs: やり直す ('redo'), 書き直す ('rewrite'), 見直す ('look again, reassess'). もう一台 stacks もう ('another') with the counter 一台 (one machine; 台 is the counter for vehicles, large appliances, and machines). In writing ~てる ('the contracted ~ている') is informal — here 考え直してる shows the casual contraction.