The most important thing about Marina is language and I think that we must not take for granted her statements that were translated from Russian to English.
We know that she knew English quite OK but we will never know what exactly she stated in Russian during interrogations and testimonies.
I believe that her statements and testimonies (when given in Russian) were not translated correctly and even she knew English, she was too scared and stressed to pay attention if the translators were translating her words correctly.
Later, over the years, she most probably realized this but it was too late to change anything, Oswald was dead and she was receiving government help so she accepted WC conclusions.
DPD, FBI, CIA, WC done everything to frame Oswald so it is very easy to believe that translations were false.