Xena may be feeling a little jealousy over the new one getting to sit in your lap. You mentioned that she had an idea she would fit in your lap and may feel put out. A basket muzzle would protect the new little one until you are sure it is safe. Training is the only way to get past this. You have to show Xena that she is still special that she still has her place but still has to show respect to you and other dogs. The only reason I would suggest the muzzle is to protect the littler one. Otherwise you have to be on top of the situation all the time and sometimes things happen that you don't expect and can't react to fast enough.
Snake Vom Eselspfad RN CGC (AKA Raina) 3/5/08
Pyrate CGC 4/1/03-5/16/12 RIP
Too many to list waiting at the bridge but remembering them all