The Berlin wall fell in November 1989, that's when Eastern Germany started leaving the Russian sphere of influence and when English might've become interesting for her.
Merkel became politically active pretty much right away, Germany was reunified in October 1990 and by January 1991 she was federal
Minister for Women and Youth under Helmut Kohl. From then on, she was involved in top-level politics, which is pretty time consuming - and which also allows you to make use of professional translators whenever necessary.
I'm not sure where or at what point she should've learned English with that biography- and whether you have a leg to stand on if you want to attribute intellectual laziness to a person just because she happens to speak Russian better than English.