She is an Arena member.
Most of her collecting specialized in Nirvana ponies I believe so she's mostly active on that part of the boards. I think she ran a Finnish page dedicated to G1 merch and posted scans of the Finnish annuals.
Unfortunately, I can't remember her username and the one of the last posts I saw of hers was stating she was moving out of pony collecting and selling her collection.
Edit: Whoops accidentally got her confused with a different Finnish member who was selling off their collection.
I still think Mari might have had an account but it may have been on the previous Arena. :x