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請問8老師， 我準備邀請妹妹來探親並參加孩子的畢業典禮。 除了邀請函之外我還需要提供其他文件嗎？謝謝！

-If your sister has her personal money to cover her travel, you just need to provide the invitation letter (she needs to provide her financial ability proof for the visa interview in this case). If you need to provide financial support to cover her costs for the travel process, you need to provide the completed I-134 with the support documents (see I-134 Instructions) to her for the visa interview.

See:

Declaration of Financial Support | USCIS