Fantastic movie, which is one of the few non English films that I have seen multiple times.
Did the mother ever find out about Alex’s deception; we see the Soviet nurse saying something about the “border opening”, and she certainly suspected something was up when she went outside, and probably when she met her ex-husband, but did she ever know the whole truth?
It’s been awhile since I saw it, but I think that yes she figured out what happened even before Lara told her. IIRC from the commentary that’s Katrin Saß’s interpretation too.
I gather she’d realized her son had been lying to her, but that it was out of love so she played along. I’m not certain she fully grasped the scope of the changes Germany had undergone; heck, even if you were uncomatose while it was happening, it was still pretty wild.