In my opinion wearing florals to a former concentration camp isnt very appropriate. Darker colours or all white wouldve been a better choice.
Having visited a former concentration camp myself, people don't dress somberly. They wear whatever they're comfortable in. I gave no thought whatsoever to needing to dress in a particular way to visit.
If she was attending a funeral or memorial service, I could see dressing in dark colors, but not for this. Anyway, it was kind of a muted floral outfit.