Qanitah is mentioned in 66:12, it's the last word of the Surah. Its plural form is mentioned "she was of al-qaniteen", the singular is Qanit, and the female form becomes Qanitah.
Saihah is mentioned in Quran 66:5 in the plural Sa'ihaat when talking to the Prophet's wives: "Were he to divorce you, his Lord might well replace you with better wives—submissive [to God], believing, pious, penitent, devout in worship, given to fasting—previously married and virgins."
Saihah is pronounced as: SA(nd) + I(slam) + HU(mble). It could be written as Sayiha to make it easier to say.