
Only you know how much fear she exhibits about going to the vet, I would advise you to make your own judgement.
I had a bitch who used to get a bit het up about going to the surgery. All went well with her first litter. The second time I mated her, I was persuaded (against my better judgement) to have her scanned, coincidentally? she re-absorbed, I was convinced it was stress linked to scanning. I did have a second litter following this episode, but she had a C section to get the last pup out. Since then, she has been far worse about routine vet visits. She is as solid as a rock in temperament and confident in every other situation.
With hindsight, I wouldn't have mated her, nor would I any bitch of mine, who is very unhappy about vet visits. You just never know how much veterinary involvement may be required during pregnancy/birth, so for me, I wouldn't want to take the chance. Obviously, vet care is needed for other things, but at least not by my intent!!
If you do continue with your plans for her, maybe Bach's Rescue Remedy or Dap could help her.
Best wishes