、。
She must have been busy, and yet she came to see me.
Literal
Busy-was-probably [despite-に], she [topic-は] me [to-に] meet [purpose-に] came.
~かったろう is a contracted form of ~かっただろう — past adjective + probabilistic. The final に functions as the concessive のに ('although/despite'), expressing the speaker's appreciation that she came despite presumably being busy. 会いに来た chains purpose (会いに) with a motion verb (来た). The contraction ろう for だろう is a casual spoken form.