How long will this go on!?

DS was soooooo easy compaired to DD. I was pregnant with #3 when we PTd him, so maybe the pressure is what we need (the pressure of not wanting 3 in diapers). At 3.5, he still uses a diaper at nap and night, but I've heard its a hormonal thing that consolidates his pee at night, so I'm not too concerned about him... He was 2.5 when he was trained, and DD is almost 2. As I was changing her morning diaper one morning, she asked "Potty train?" ... so I decided to give it a go... and it was going well.

I've read other posts about how the child will pee/poo with nothing on, but not if underwear is on. And this is where we are with DD. Putting a dress on with nothing underneath won't work, because she goes potty fine, but doesn't lift a dress to go... so the dress still gets wet. She has no problem with either pee nor poo when she's naked... she doesn't even tell me when she has to go... shell go sit on the potty and come tell me what she's done. That part was easy, it took about a week or maybe two.

Here's my method that worked so well with DS: First few days, naked on bottom... feed lots of salty snacks (pretzels, chips, saltine crackers) and juice and sugary drinks not normally given so frequently. The idea is to get them thirsty and wanting to drink a lot so he or she will have to pee. And set a timer to take them to the potty every 15 minutes. Again, the idea is to get them to associate the feeling of having to go with going. After a few days of naked-bottom, once I feel the concept of using the potty is grasped, I'll put them in training underwear (the thick cotton bottoms, not pull-up diapers) and still take them to the potty every 20-30 minutes. Reward is a PEZ from a special dispenser (DS had Spider-Man, DD has Hello Kitty).

DD will use the potty for pee and poo when nothing is on her bottom. She even knows when she hears the timer ding that it's 'potty time,' though I still have to physically lead her to the bathroom. She pees every 20 minutes, sometimes a lot simetimes a little, but she pees something every time. But she won't go by herself, and she definately won't tell me if/when she has to go... if I don't take her and pull the underwear down, she'll wet herself without saying a word. Sometimes she poos in the potty, sometimes she waits until she has a diaper on at naptime to poo. Right now, that's not my concern. I want her to either go by herself or at least tell me when she has to go when she's wearing underwear. This has been going on for about 2 months. DS had it after a few weeks, except for poo... he took a while to poo in the potty, but at least he held it until his diaper at nap. But I digress... this is about DD.

Sorry this is so long, but should I just keep going with this and hope it will eventually click? Should I stop completely when we're halfway there? Is there something I could change to help her get it? Honestly, I'm getting sick of taking her every 20 minutes...

Whether you agree with spanking or not, we spank our children as discipline. But I'm wary of spanking her for wetting herself because if she truly doesn't get it, then she can't help it... and spanking her for something she can't control won't help (but the fact that she goes on the potty when naked leads me to believe she *can* control it.)

Can anyone help?