。
She'll be along right away.
Literal
She [topic-は] right-away come-along.
やってくる ('come along, come over, arrive') is a productive compound built on やる + くる. The やる contributes a sense of motion that's directed and active rather than passive — she's not just appearing, she's making her way over. Plain non-past as future prediction. Common in narrative and conversation alike: 春がやってくる ('spring is coming'), お客さんがやってくる ('guests are arriving').