Well, as young as your baby is and as small as she is, I would wait as long as possible. With the weather turning cold, she's going to need all of the hair she can get. I'd be most concerned later with keeping the hair from poking her eyes and keeping her ears, nails, bottom of foot pads, and feet trimmed.
If it were me, I'd look for a private groomer that was experienced in trimming yorkies rather than a chain store groomer. I wouldn't go to a chain store. I don't even believe chain store groomer's are licensed, so you want to place one as small as your's in as safe of hands as possible.
