It was much better when that used to be the case. The "friend" relationship, even when the adult has no bad intentions, can so easily be misread by students. Better that personal issues get referred to trained counselors.
Besides which, this is a substitute teacher. It's just not smart to be anything but aloof and just do the job...keeping the kids safe, maintaining order, teaching the lesson, leaving the room in one piece. If she can "friend" the students, so can anyone who walks in that room for a day.
She has problems with her judgement. She should resign.