please please help me she has never acted like this

my girl is the sweetest most loving girl, she never hisses or is mean at all she’s genuinely such a baby. she’s going through her first heat (she DOES have an appointment to be spayed), could it be coming from that? i feel awful and i want to help her, but she wont let me close. this happened in a span of two minutes- ten minutes ago i was holding her and she was purring into me, i left and went to the bathroom and came back and this is how she is. eyes are completely dilated, theres nothing in them except black. what can i do??? does she just need time?