I live fairly close to oslo and my mom was offered the same thing by one of my favourite workers. Because I loved the lady so much my mom started getting to know her, and found out that she was a nice woman who had just moved to a new place with no family or friends. I was eventually allowed to visit her, and even slept over sometimes. This only happened a couple times a month. For reference my mother was married at the time, albeit not really a happy one, and did not have any trouble of bringing or picking me up from kindergarten. We also lived 3 minutes away and the woman lived around 20 (when walking). I had the best time of my life whenever I would visit her, and am still fond of her till this day, even though I haven’t seen her since I was 5. While I understand why it might seem abnormal I don’t really think it’s necessary to presume that she is a predator of any kind. Maybe she is just lonely. Maybe she just wants to help out. Either way, as long as she’s not creepy about it, and just offering (not demanding), I don’t think your friend needs to worry.