Almost every child goes through a period of being interested in the potty around 18 months old. Sometimes it lasts a few weeks or months, sometimes just days. She may or may not be ready. Most experts would say she's too young to be truly potty trained. It depends on what you define "potty trained" to be. Most experts say that means your child can do everything by herself - recognize the urge to go, go to the bathroom, pull down pants, sit on toilet, wipe, flush, pull up pants, wash hands, dry hands and go back to playing. Most kiddos can't do all those things by themselves at just 18 months -- it's usually closer to the 3rd birthday. So experts will tell you that your child isn't potty trained but rather you are 'trained' to help her. There's nothing wrong with that and many parents do it... it just comes down to your defination.
IMO, let her explore the potty and even use it a few times a day. Every 1/2 hour is too much pressure, though, I think. She doesn't "get it" yet. If she's sitting on the potty every 1/2, when is she playing? I think it's better for her to just continue playing at this age because there is a TON of learning going on in random free play at this age.
I know plenty of parents who have "trained" their child as young as yours but in reality (and they'll admit it) they just have their child in a regular feed/sleep schedule and they've learned the visual clues that their child is about to pee/poop and get them to the toilet on time. Or if the child does recognize the feeling and tell them, the parent still has to do almost everything for the child - carry to toilet, pull down/up clothes, help wash hands, etc.