Rubina is looking forward to--America.

Rubina is looking forward to "going to" America. This phrase is used to express her anticipation or excitement about visiting America in the future. It indicates her intention or plans to go to America. Comparing the options, "going to" is the correct choice because it correctly conveys the future action of Rubina's journey to America. The other options, such as "go to," "going," or "go in," do not accurately convey the sense of anticipation and future action indicated in the original sentence.