I would suggest to make sure she gives as much attention to her dog as much as her baby and include the dog in with baby time after a week or two of bringing home newborn baby. What I mean is let the dog get used to baby smell on them before introducing the newborn to yorkie. Then just a few minutes at a time or less let yorkie smell newborn and if behaves well praise her profusely and tell yorkie this is the new member of her pack. If at first she growls at it or tries to bite tell her no and take newborn away for awhile. Then try it again.
Once yorkie is comfortable with newborn let her hang around baby while changing her diaper on the floor. (that's a big maybe and decision left up to mama
)
But always use caution. In time and overall I think the yorkie will be fine with the baby. Just use caution and take time in introductions. And make sure they don't neglect the yorkie in the process - always, always include her when baby needs attending to and praise her for any good behavior toward the baby. (for example, if baby needs fed let yorkie sniff the baby or tell her it is okay and let her hang close by while not actually close to nip or lick baby. Do not shoo her away constantly or ignore her attempts to get close to mama.) There maybe several introductions before all become one.
Hope this helps.