Thanks in advance!
I would think you would watch for widening of her pubic symphsis. Too bad the people you got her from could not give you information to plan with.
I would have a vet lined up in case there are complications.Harkness and Wagner in The Biology and Medicine of Rabbits and Rodents describe how the pubic symphsis begins to separate late in the pregnancy due to the hormone relaxin. About 48 hours before birth, you may be able to feel a gap of 15mm or so. At birth it can increase to 2.5 cm (1-1.5"). "If the first breeding is delayed past 7 or 8 months, the symphysis separates less easily, and fat pads occlude the pelvic canal. Such impediments may lead to dystocia and death, especially when small litters of large young are involved)."
- And got the T-shirt