A question for Sisters...?

Wa alaikum salam wa rahmatullahi wa barakatuh. Really based on hadith or ijma of ulamas (fatwa)when a woman becomes pure before sunsets,she must offer zuhr and asr together,because the last two prayers can be done later on after asr and before maghrib.It means in normal situation we can put off zuhur not in time and be done on the time of asr. Besides that we could be forgotten to see whether we become pure or not in time.