I agree with Andrew. In the strict laws of the English language, her is incorrect. But as a native myself (British) I think most native speakers would use her here. For example: "Me and Peter are going outside" is 'technically' incorrect but sounds way better to my native ears than "I and Peter are going outside" or than "Peter and I are going outside" (In my opinion the third of these three sentences is valid but sounds super formal/posh, the second one I've never heard). Likewise here I'd be more likely to say "you and her think" than "you and she think".
https://data.grammarbook.com/blog/pronouns/tis-i-or-tis-me/ this has an accurate answer to this question
This may answer your question: https://data.grammarbook.com/blog/pronouns/tis-i-or-tis-me/
Think of 'you and I'. You don't say 'you and me think'. I'm also tempted to say 'you and her' or 'you and me', although I am not a native speaker. It just sounds more natural for some reason, maybe because people use it a lot. But normally you should use the nominative (subject) case, and not the accusative (object) case, hence it's 'you and I' and 'you and she'.
If you want to use correct English ONLY, then be consistent and also give the right options. Some questions are penalized for a simple english error despite the essence of the indonesian being understood. And then some questions do not even have proper english. That is terrible consistency.