Thanks aunt! 小姨 refers to maternal aunt, which Chongyun refers to Shenhe as in the Chinese voiceover in game. See this wiki page for more info.

Sleep at your house for a night? Of course that's alright!

As long as you is fine with it! I'd even be happy to stay one week! 小姨 is being used as a proper noun, but the literal translation is aunt, which is seldom used as a proper noun in English. It can be translated to "aunt Shenhe" or "you" when used like this, but I went with "you" since Shenhe's name isn't mentioned.