I was wondering if this is resource guarding you, but if it is the same when you are not present, that is very odd.
Is there something else in the environment that she might be guarding? Did she get accidently hurt recently when playing with your partner? Maybe some conflicting feelings of wary-ness (I'm going to get hurt), then moving on to wanting to play with her buddy.
Gryffon Vom Wildhaus
BH, OB1, TR1, AD
Rottweiler/Hairy Dog mix?? 2004-2015