Ok, I am going to say this as nicely as I can. Rosie was PISSED!
Oh my gosh she was mad mad mad. Lol. She even barked, growled, and tried her best to get at Mikki. Then she would get on her blanket and turn her back to me. She was livid in the thought that I brought home another female. It was a rough week. A rough rough one. I even started to think I had made the wrong decision. She would try to fight Mikki the entire time. BUT then things started to settle down. All it took was Rosie getting Mikki down during one of the fights. Mikki was laying on her back and Rosie was the one who had her pinned down. At that point, it was obvious who was the dominate female. And things started getting better.
Now, they run through our house playing, play tug of war, see who can get the bully stick the fastest, etc. We still have an occasional fight but nothing like it was at first. Now, I actually think they kinda of like each other. My friends male Yorkie came over to play and growled at Mikki. Rosie got all up in his business. It was like she was telling him "Hey don't mess with my sister. That's my job!" Lol.
It will be tough at first. There is no denying that. But if you want it to work then it will. I asked a lot of questions when things happened and that helps you to figure out how to handle things. (Thanks Ladyjane!
) Like I said in the previous post, just make sure you do everything with Gidget first. She is used to you being there, the new pup isn't.
BTW, Rosie is 4 and Mikki is 1. Rosie is 5 1/2 lb and Mikki is 3 1/2 lb. You will be surprised how well a small one is able to hold their own. So, I don't think the age and size will be too much of an issue.
If I can help in anyway let me know. You can PM me at any time!
Go with your heart. And trust me, if Rosie can handle this, any pup can! Lol. Can't wait to see what you decide to do.