3/4 of an ounce....WOW! That is super tiny and seems unlikely,but I'm no expert. It's hard to tell from that picture, but even the littermates look a bit "plump". She said that the biggest was 2oz...it is hard without seeing them in person but they do look a bigger than that in the picture.
Do what you are comfortable with,though. If you decide to not buy from her,take a look at some of the great breeders that YorkieTalk has!
Tammy