New Dog member

Hey guys, My question might be one you hear every day but here goes.

We just adopted a new dog from the Humane Society. We already have one dog, Mazie who is a mixed terrier that we've had for about 5 years. Mazie is a very timid, submissive unsocialized dog. She was very well trained (or abused) when we got her as she did not even bark for the first year we had her. She did not jump on furniture and when placed in the bathroom she did not whine or make any noise.

We just adopted a new dog that we named Delilah and she is a Collie mix. Delilah is alost twice Mazie's size and a puppy. She does all the puppy things, runs , jumps, nips and likes to put things her mouth. Mazie does not like Delilah but she is not Alpha dog enough to put Delilah in her place. Mazie may bark but when Delilah comes around she cowares and yelps. Mazie remains on the couch and will not move from there unless she knows Delilah is not in the room. Delilah will stare at Mazie and walk circles around our coffee table right next to the couch and then when she feels like it, nip at Mazie but Maz has never been hurt by Delilah. 

So what kind of techniques can I use to get these two dogs to get along? I have been placing Delilah on her leash and placing them together and every time she lunges at Maz I give her tug. I'll also place Delilah in her kennel and have Mazie on the outside and feed them both some chicken but I have not tried to feed them together. But other than that I have had to keep them seperate. I want Mazie to have some seniority over Delilah but she is too timid and submissive.

Any Suggestions or additional techniques that I can try?
 
*Edited to remove links*