It is not hard to see what she was thinking. It has been preached and pushed for decades here as well.
1. Multiculturalism. No culture is better than any other, except Western Civilization, which is blamed for all ills of society.
2. All people are basically good. (a very bad premise)
3. All people are the same all over the world. (Another bad premise)
Given these false premises, why wouldn't you embrace open borders?
Indeed. These countries aren't sending their best. Not even their 'normal' people. They are emptying jails, asylums and hospitals to foist their problem off on someone else.
If they wanted true diversity and successful immigration they should be charging each entrant a million dollars/Euros/whatever.