Let them meet in a neutral area, somewhere that your current dog isn't going to feel 'threatened' such as in the room she sleeps in or something (you know best her comfort levels and where she is comfortable or where she isn't). Let them meet outside in your yard first? I would take your current dog to the shelter and let them meet there before adopting. If your dog gets a long with other dogs well you shouldnt have a lot of problems adding to your pack. When you do get them home and in the house. Let your current dog call the shots and let the new dog know what is acceptable and not acceptable if your current dog doesn't like other dogs in her personal space (I have 2 dogs that don't like to play or have another dog bothering them so I let them tell my puppy that 'hey i dont like you rough housing with me, so my puppy learned that the other 2 didn't like playing like that so he seeks me for all play interaction, which is what I wanted anyway) so if it is a correction like that, let them do it as long as it isn't an aggressive way, I'm going to eat your head off kind of correction, you should be able to tell the difference. You will need to be the pack leader. You will have to help your dogs figure out their places in the pack BUT you are the pack leader and YOU call the shots. I have had to put my BC pup in check b/c of some jealousy with my new rescue BC. He was guarding his food (normal behavior) but when he snapped at the new dog, I let Ace know that was not acceptable and I'm the boss, it stopped immediately. You have to be very strong and you have to catch and correct behavior at the right time... the second it starts.... not after the fight starts, you have to catch it right away. If you can catch it soon enough, all it can take is a 'HEY' from you and break thier concentration, sometimes that is all it takes or put your self in between them and say HEY or NO!
I may be going off topic here.......... but how does she act around 'hyper' dogs? Does she correct them? If so , how does she do it, what is her body language?
I'm a little late responding... sorry.. Did you get another dog already?
Good luck!! Hope that helps?