New puppy with older dog

Hi everyone. We have a 3 1/2 year old Yorkie bitch who is a lovely little dog but still has some problems. She got jumped on at a puppy class which has sparked fear/aggression. With perseverance she is getting better but still has her moments. We are thinking of getting a puppy and one of the (many!) things I'm concerned about is whether the puppy will copy Lucy and if so is there anything I can do to avoid this?
Also, if anyone can suggest the best way to introduce the two of them that would be a great help. Thanks x