I think she's also quite anxious about her new home, and should settle down after a few days. It's hard to poo when you're anxious! When you take her into the garden to do her business, be calm and gentle with her, and when she does her business give her praise and stay with her outside for another five minutes or so. My new pup would usually do another wee/poo a few minutes after doing the first one! Going out in the garden when she doesn't need to go and playing some games with her might also help to form an association with garden and relaxation/enjoyment.