
We had a singleton bitch, called Canuck (her mum was Canadian-bred and also the French-Canadian thing). It's hard not to spoil them once mum is off and away and until she was simply too heavy, I used to carry her around with me all the time! She looked so sad alone in the whelping box and she was too small to run with the adults. Fact is she was a real madam and the others used to respect her big time, skirting round her! Other than being a prima-donna, she didn't really have what I'd call behavioural problems. We kept her although she didn't really live up to expectations so she was spayed (plus she started having a season every 5 months, starting bang on 6 months which wasn't normal for mine).
There's no reason why your singleton puppy should have 'behavioural problems' in truth.
ps We had a heart-stopping episode with her when out across the fields, they put up a herd of deer which I'd not spotted in time to get them on their leads. They did stop however, apart from Canuck who took off across two fields baying her head off. She was only 9 months and we don't do that kind of thing at 9 months!! Taking the others home my husband set off in the direction she went and by the time I came back to join in the search, he met me with her on a lead, looking 100% pleased with herself. Clearly she's lost the deer and was backtracking, as hounds will do. I met the local gamekeeper on the way back with the others and told him we had one loose - he said oh it's okay, I have no traps out in that direction