Here is a list of names other than her name Walter has called Astrid.
Please add any I missed
I read in an interview with Jasika Nicole, actress who plays Astrid that Walter Calls her this
in an upcoming episode, only look if you want to be spoiled.
Spoiler (Click to reveal/hide)
Afro, funny because she does kinda have one. Walter then realizes it and makes a funny comeback, like oh no, now they will think i am a racist.