I`m not an expert but there must be quite a few people around the world who have become pregnant while on anti-malarials (all those honeymoons in exotic places). I wouldn`t be too worried if it was me. Did your niece climb Kili? I remember people taking Diamox as a preventative for altitude sickness for the whole time they were there. I always thought that was a bit strange as it`s a diuretic and that`s the last thing you need at altitude. As she only took two, I wouldn`t be too worried if that was me either (but I`m not an expert - Sqad is).