First of all, welcome to Yorkie Talk. There is a wealth of info here and some very experienced breeders. You have been posting back and forth with one of the most experienced breeders on this site, so she knows what she's talking about.
The title of your thread really highlights your lack of experience. This is such a basic question in breeding that it shouldn't need to be asked if you are setting out to breed your girl. This, and much, much more should be known well before even considering breeding.
Yorkshire Terriers are not a breed that you can let Nature take its course with. Intervention, even in textbook pregnancies and births, is necessary and one must be aware of the signs of distress in both the Mom and pups to avoid disaster. I would add that complications occur as often as not. Knowledge and preparation is essential or you could likely lose your girl, the pups or both.
There is a current thread in the breeders' forum now where someone let the Mom cut (chew) the cord and she wound up chewing the baby's foot off. Just one of many, many tragedies that could be avoided if the breeder was experienced enough to know what to do. All you need to do is read some of the threads here and you'll see just how wrong things can go.
Mardelin was right in saying that you don't have enough time to learn even the basics of what you should know to go ahead with a breeding at this time. And, if you're doing this only for the 'experience', I would tell you that this is an experience you could do without. You must ask yourself if you trust your own knowledge well enough to place your girl's life in your hands.....which is what you would be doing by breeding her.
If you think you want to consider breeding, you must get serious about acquiring all the knowledge you can in advance of actually pursuing it. There are many good links posted in many of the threads here and one of the better one's that I have handy is this one.
Dog Breeding and Canine Reproduction by Debbie Jensen. Dog Breeding and Whelping guide for dog breeders.
Along with the advice Mardelin gave you, I would recommend a couple of books....."The Complete Yorkshire Terrier" by Joan Gordon and also "The Joy of Breeding Your Own Show Dog" by Ann Seranne. Despite its title, it's not only for those aspiring for the show ring. There is some very good information there for any breeder.
I strongly urge you to just spay your girl and enjoy her. Unless you are completely dedicated to breeding, it's just not worth it. Along with the knowledge and expense required, be prepared to put your life on hold for months, and that's with all going well. With complications, tragedy and heartbreak may be all you get for your efforts.