happy belated birthday.
wait is her b-day on the 14 and 26?
This isn't the most accurate analogy, but it works: Think of the whole Russian/Western calendar as a really BIG time zone. When it was 14 June for Maria, it was 26 June in the west -- just like how when it's 9:47 for me in Michigan, it's 12:47 in Los Angeles. It's the same moment, but we label it differently.
Now imagine everybody but Russia switched to daylight savings time in 1900. That made Maria's birthday 27 June outside of Russia.
Celebrating Maria's birthday on 14 June in the west is like setting your clocks to New York time even though you live in California. You'd end up eating your lunch at 9:00am instead of noon, and you'd celebrate New Year's at 9:00pm instead of midnight. It just doesn't work that way. If you live in the US and you want to wish your friend in Australia happy birthday, you'd wait until the right moment in *their* time zone, not yours. That's why it doesn't make sense for us to observe Maria's birthday on 14 June -- on Maria's calendar, that same moment would be 1 June.