Just to clarify what was said:
they think she had been there for several days, under heavy snow.
they said she was fully clothed.
they think she returned to the flat as her belongings were there (hopefully they have considered someone could have put those back afterwards, to make it look like she left them there herself)
they want people to get in touch with ANY information even if they assume the police already have it...better to be told twice than not at all.
So if anyone did see anything - please email them or call them. The police website is linked at the bottom of BBC news pages.