Is performing two rak'ahs of qiyam al-layl, by reciting half of the [daily] portion in the first rak'ah and the remainder in the second, while sitting most of the time due to fatigue, and spending the rest of the time in seeking forgiveness (istighfar) and remembrance (dhikr) until Fajr, considered qiyam al-layl?

Performing supererogatory prayers while sitting is permissible, even without an excuse, but its reward is half the reward of one who stands, except for those who are unable to stand, for whom the full reward of one who stands is given. Qiyam (definition) al-layl (night vigil prayer) is the supererogatory prayer performed after Isha until the appearance of dawn. Whoever prays two rak'ahs or more during this time has performed Qiyam al-layl. What the questioner is doing is considered Qiyam al-layl, and she should conclude it with a single rak'ah to make it an odd number (witr).