chihuahuas introduced-aggresion and humping

Question
We have a 1yr old female chihuahua who is not fixed (we would like to breed her).  She is a great dog but will bark often and sometimes get very upset and growl at other dogs or animals. Other times she's fine and usually affectionate.  She does hump her stuffed animals and occasionally tried to do it to my daughter's leg. We also play tug and fetch with her animals which she seems to like.  
Recently, someone asked us to adopt their 9 mo old fixed male chihuahua.  He is very sweet, rarely barks, obedient and on the shy side.  We want them to get along.  He seems more scared of her-she seems wary and more aggresive to him.  This is the 2nd day they have been together.  How can we facillitate them becoming play mates?  Our female dogs mom lives across the street and they love to play together.  will she ever feel that way with the boy dog.  Also he is very well potty-trained. He will wait and only go outside all at once. She, however, will go on walks and stop and go only a few drops at a time.  Is that normal? Should we not let her hump?  We just thought it just her playing with her toys mostly and that we shouldn't interfere.
thanks for your suggestions

Answer
Hi Afton, Generally, humping activity is a sign of dominance. It is common in our little girls, especially those that are not spayed. It can be an embarrassing problem when they do it to a person. We do not want to let them try to dominate friends and relatives, so you can correct her with a simple no or a touch to the scruff of her neck. I would not worry about her new house mate, they should get along fine. There is going to naturally be a time of adjustment when they decide who is the pack leader, below you and your family members. It will probably be her, so be sure you do not let her get too aggressive with him.  If she growls or snips at him, make a noise "shhh", "AHHH", or something simple to get her attention and if she grabs him, gently touch her on the scruff of her neck and tell her no. The will soon become close friends and you will have two very nice little dogs to go on long walks with. Enjoy every moment of it. Leave me some feedback and keep me posted on how it goes. Regards, Susan