Aw man here we go. Another white knight jumping in without trying to understand anything about the relationship.
You realise she saw Ai strangle Hina and threaten to throw her by the window right ? I doubt anyone sawing will think the two girls have an heathly realtionship.
"Healthy" is a subjective term that can vary greatly by time period and culture. Also, while any outsider can pass judgment, only those in the relationship can truly define what they have.
But I shall admit that, faced with such a situation, I would have said "huh" and carried on with my day. My business is mine and other's, even my friend's, is their own. Unless asked for help I shall not interfere.
It is this line of thinking that led to my former comment.