Please do not use punishments or time outs while potty training. She's not trying to piss you off (pun intended) and, therefore, shouldn't be punished for when she has an accident. Praise is all that should ever be used. If you turn potty training into something she should fear or get anxious about, you're going to make it that much harder for the both of you.
All it sounds like is she isn't that well potty trained; she's doing a decent job, but she's not fully there. No biggie. Put her in pull ups if that will lessen the accidents (and lower your frustration). For whatever reason, it seems to be taker her longer to gain bladder control but she'll get there.
ETA: So, just some thoughts:
I don't know how old she is or how long she's been potty training, but since she seems to be pooping on her own with no problem (which is odd - it's usually the 'pooping' parents have the heartache over), does she NEED to tell you when she has to go pee-pee? Or can she just go?
Maybe you can try switching the reponsibility from 'Tell me when you have to pee' to 'Tell me when you've gone pee-pee in the potty'. That might, hopefully, gear her mind to thinking more about her bodily functions rather than trying to remember to tell you she has to pee (because at that point, it may be too late).
We used pull-ups on our son (who's now 4) when he was potty training. They're not diapers, but more like "super absorbant" undies they can pull off and on themselves. Other kids respond to "getting" to wear big girl/boy undies. Kids are different - you may have to try a couple of things to find what works for them.
And again, she just may need more time to get the pee-pee thing under control.