How come she doesn't have a Russian accent?
Mila was said to have moved from Ukraine to the United States when she was 7 years old. She didn't know or speak English what so ever at the time.
https://www.dailymail.co.uk/tvshowbiz/article-2140183/Mila-Kunis-cried-day-speak-English-moved-America.html
I heard that if you begin to learn English after the age of 12, the chances are higher that you'll retain your native country's accent.
https://www.reddit.com/r/AskReddit/comments/19ysru/how_did_mila_kunis_learn_english_so_late_in_her/
So 7 years old in the greater shape of things, probably isn't "too late" to learn how to speak English and not do it with a strong accent.
https://www.youtube.com/watch?v=sJhPa4lMLDo