We did every 30 mins one week then slowly it stretched out, but she did also get confused sometimes when she started having underwear on. Didnt make a big deal out of it just said “uh oh, its ok, next time tell mummy you need a wee wee” and moved on. If we went out then id get her to go potty before we left and just after we parked the car then id time it making sure i have access to a toilet somewhere within the timeframe id know she would go.
We started with every 15-20 mins then built up to every half hour. We did the Oh Crap method and it worked really well.
It's usually every 15 mins, asking and encouraging her.