There are loads of potential sightings of Melanie between 1am and 2.15am, but AFAIK none of them are confirmed sightings.
The sighting at 1am might be genuine, as might the Walcot Street sightings, but I'm not sure they were made by people who actually knew Melanie.
JMO but I'm going with the 1am conversation with her friends as the last absolutely confirmed sighting.
Change the first and third 1ams to 1.10am in this post.. I'm getting my timeline confused!
*1.10am last confirmed sighting*