If you are not planning to marry the child's mother, I am afraid you will have just about a zero chance to have her visit the US.
If you were planning to marry her you could bring her in on a K1 fiance visa, for example. It would take months for the process, but she would eventually be allowed in. Do not do this unless you are going to be married!
Getting a visitor's visa for any Dominican is next to impossible. If the mother were well off, had a long bank account history, a business, owned a home in the DR, etc, she might have a slim chance of getting a visitor's visa. In your situation, the child and you being US citizens will demonstrate to the immigration officials that the mother will wish to stay in the US and
will not grant the mother a visitor's visa.
More information on K1 and Spousal visas can be found at:
www.dominicanstotheusa.com
One thing that might come into play here is that the child might be able to be the sponsor for her mother to come in permanently to the US. I don't know much about that process, other than that it can take years. The web site above should have more information on that approach