Try and see this from the point of the medical staff, someone has been admitted after a suicide attempt and then refused to see a psychiatrist and self-discharged instead. From their perspective its very very high risk behaviour and if she leaves and kills herself without them making an attempt to bring her back to a place of safety it's their necks on the lines, and her death will be on their conscience. They are legally obliged to do everything in their power to see that she's safe, including calling the police to bring her back when she self discharges without having received adequate care.

On a very not-legal note, it sounds like she's trying to brush this off as not a big deal, which is frankly very dangerous. I think the best thing you can do as her friend is to encourage her to accept the help she's being offered, which she very clearly needs. I'm sure you both want to get back to your lives and move on, but please don't underestimate how unwell she must be to make a suicide attempt so serious she needed medical attention. I hope it works out well for both of you