I am exhausted

Spent 3 hours yesterday evening dealing with a very unhappy little 8yo. She was upset with me because I took her home when she had a tantrum at my dads house because I wouldn’t let her swim in his pool since no adult could supervise her at that time. Tantrum then crying all the way home then 3 hours of drama going around in circles with her until she finally fell asleep. So... I’m exhausted 😴 I feel like I need some kind of debrief with her but she’s happy playing right now so I don’t want to drag it all up again

She just doesn’t seem to take it in when I tell her I’m not going to hit her... when she’s calm she looks like she understands and then she has a meltdown and seems to just forget in the moment that she doesn’t need to be scared of me. She acts out, then FREAKS out about the fact she acted out and loses her mind when I go near her like she thinks I’m going to do something horrible. She’s clearly used to that crap from our aunt and doesn’t get that I’m not going to do that to her. I need to get her to realise that we can deal with an outburst calmly...

Until she understands that I guess its gonna be tantrums about tantrums around here.
I am trying to arrange therapy for her but its taking a while and she says she doesn’t want to do it. I’ll make it happen but in the meantime she’s booked in to big sister’s very unqualified home therapy I suppose