When I had just two I never thought in a million years that I would get a third. Then I saw CoCo's picture posted in the Yorkies for Sale section here on YT and it was like a lightning bolt hit me! I could NOT get her out of my mind and everyday for almost 3 weeks I would look to see if she was sold and she wasn't because she was WAITING FOR ME to take her home! Now that I have three, I can't imagine why I was so worried. Three is no harder than two, just more expensive! If you have the means to take care of her, go for it.
I believe that things do happen for a reason and this little girl's first adoption fell through because she's meant for somebody else and 'somebody' may be you.
Do your homework and ask the rescue groups all the questions you might have because you do want her to get along with your other two. But if she's as sweet as she looks, she will make a great addition to your family.
I'm hoping that my hubby will someday let me have a 4th because I want a Biewer. He says I'm nuts but I'm just IN LOVE!!