[name_f]Magda[/name_f], [name_f]Lena[/name_f], and [name_f]Maggie[/name_f] (probably in that order. Maybe [name_f]Lena[/name_f] then [name_f]Magda[/name_f]) from your list. I love the Scandinavian [name_u]Malin[/name_u], too, though, which I also think would make a great nn for [name_f]Magdalen/name_f, since it’s the Scandinavian form. I can totally see [name_f]Magdalena[/name_f] “[name_u]Malin[/name_u]”.
I don’t get [name_f]Margaret[/name_f]/[name_f]Marguerite[/name_f] as a nn for [name_f]Magdalen[/name_f], though. The only thing they have in common is that they can get the nn [name_f]Maggie[/name_f]. [name_f]Magdalen[/name_f] to [name_f]Maggie[/name_f] to [name_f]Margaret[/name_f] is a pretty big stretch, imo. [name_f]Magdalen[/name_f] and [name_f]Margaret[/name_f] are totally different names.
I knew a [name_f]Magdalena[/name_f], she went by [name_f]Magda[/name_f] and I always loved her name. We shortened it to [name_f]Mags[/name_f] sometimes.
The thing with nicknames is that they don’t have to be rigid. I could easily end up calling my [name_f]Magdalen[/name_f] [name_f]Marguerite[/name_f] at times. Or [name_f]Birdie[/name_f] or [name_f]Lulu[/name_f]. Many of my nicknames given to me by folks throughout my life have only had a tenuous tie to my first name.