User blog comment:B214/Question and Answers 4/@comment-4547267-20150109152904/@comment-24468758-20150109165853

You know she accepted his dream of having a harem at the very beginning already and after that she became his girlfriend, so do you really think she still needs to officially consent to it? If you still aren't convinced:

She is okay with the other girls sleeping together with them, having a bath with all of them and Issei even goes on dates or something close to it (regular shoping for clothing or something like that) with them.