。
She might agree, or she might not.
Literal
She [topic-は] agree might [and-し] not-agree might.
Repeats ~かもしれない on both sides of し to express total uncertainty — the outcome is genuinely up in the air. The particle し here lists two parallel possibilities rather than its more common use of listing reasons. The casual contraction しない (rather than 同意しない) for the negative side is natural in speech, where the repeated verb gets dropped.