I guess wearing Abaya and a scarf would be for the best...which she would wear for only 5 hours or less of her life!

"but dotdot poligamy is illegal in europe but you do not see the police arresting saudis when they just pass through"

First of all not all muslims have more than one wife..
they are allowed to do so, but most of them are married to only one woman...

Secondly.. Europe countries are non-religion based countries.. I means it has no formal state religion like we do in Muslim countries..

So our rules must be driven from our faith...Us being religion-oriented countries..
So, ofcourse our rules would be more on the religious side...

You come here knowing that fact, we live by islam..
Our religion is guiding us in every aspect of life..

It's no only practised in mosques.. like other religions do..

"What would be an unpleasant incident? Do they lash the women who do not wear an abaya?"

They will never lash any woman for not wearning abaya..
but ofcourse there will be some kind of procedure..
They might be detained or something of that sort..

So why make a fuss over something that won't take up much of her energy to do??

Wish you a safe trip...