Dog behaviour help please?

Miss B is a 15 month old homebred *****.She has been well socialised and attended ringcraft classes designed for show dogs. She has been shown in the breed ring several times and been confident and well behaved. She lives with our 9 other dogs in the house with the family. Our dogs vary in age and are all well trained show dogs or ex show dogs. Some have gone on to compete at agility with considerable success.

Miss B is exhibiting some strange behaviours which I have not seen before. She is very attached to me and is always to be found next to me. She has an excellent recall. She can be a little bossy towards the other dogs, barking and lunging at them on occasions for which she receives a sharp 'no' but no other punishment as this usually stops her.

If I remove her from the pack for an individual walk or outing she is fine. However, if I remove her for individual training she begins enthusiastically but soon stiffens and takes herself off into a corner or away from me. These are basic sessions, 1 a day, which last approx 5 mins. Lots of positive renforcement is used with no negativity. She learns well but seems to be put off by the fact that she is learning whereas most dogs would be excited. She doesn't shake or lick her lips and still gives me eye contact without cowering. If I let another dog into the room for dual work she comes and goes as if half of her wants to join in and half of her refuses to. I have never seen this behaviour before. Any help with it would be much appreciated. Thank you