Ok woah. First of all, it's not her puppy, you have a life, you are caring for your dogs and a new litter and a job so she needs to KICK BACK.
Deposits can be returned lol I'm just saying.. puppy buyers need to understand that politeness is key and that breeders have enough on their plates without whiney future puppy owners. Many breeders wouldn't have even mentioned this puppys problems in the first place so she should be thanking her lucky stars.
I would re-iterate that puppy placement has NOT been decided and perhaps instead of doing one on one emails with her about this puppy, send regular weekly GROUP emails to puppy buyers with information on ALL of the puppies signed with your blog at the bottom so they can check for status updates there. I'm sure she means well.. but I think needs to be be reminded that it's WAY to early for puppy placement decisions and you just don't want specific people to get attached to puppies that might not suit them the most.
Oh and perhaps remind her that you are very busy and it's easier and less stressful to update your blog which is available to all buyers then it is to respond to personal one-on-one emails.
How often do we ignore work emails to play on facebook? It's natural. it's normal. This wasn't a life/death or serious issue.. just a daily puppy sniffles thing and frankly, although she is perfectly within her rights to want a response and of course we all want to know EVERYTHING about the litter of our future dog. I think getting all upset over it is a tad dramatic.
A private blog or facebook page
solely for puppy buyers could also be useful. Update it once a week or as these things go on and change..everyone gets to see it. Nobody feels left out that way and questions can be posted there rather then email (it's so much easier to deal with questions ONCE instead of constant back/forth private emails) and they can keep the page after to post updates and check up on siblings