2.5 year old refuses to wee in Potty

My daughter is 2y 6 mo - she goes to my sisters and my best friends house for childcare and has shown an interest in the potty at both houses by sitting on it but not actually doing anything. They have both told me she shows all the signs of being ready to potty train so we started yesterday. Yesterday she wouldn’t even sit on the potty and would just scream if I suggested it. Today she has sat on the potty a couple of times for a couple of seconds. It’s now midday and she has not done a wee on the toilet or had an accident. I’m concerned by the fact that she is holding it in. I’m scared she’s not ready but everyone else is telling me she is and to just be persistent but I don’t want her to end up with a fear of the potty or bladder issues caused by holding it in so long.