。
She lies often, so she can't be trusted.
Literal
[topic-は] often lies [object-を] tells [because-ので], cannot-trust.
嘘をつく ('to tell a lie') is a fixed verb-noun collocation — note the verb is つく ('to attach, set'), not 言う ('to say'); a Japanese speaker tells a lie by 'attaching' it. ので is the softer, more reasoning-oriented 'because' — it links the observed pattern (frequent lying) to the conclusion (untrustworthiness) more diplomatically than から would. 信頼できない is the negative potential of 信頼する ('to trust'), giving 'cannot be trusted' or 'unable to trust' depending on context.