According to the credits for episode 12, the severe nurse was played an actress named Ingrid Torrance. She is not the Queen of Hearts from episode 17, in which the credits list the Queen of Hearts being played by another actress: Jennifer Koenig. This knowledge also discredits the theory that the Queen of Hearts is Regina’s mother, Cora, who is in fact played by Barbara Hershey in the credits for episode 18. There we have it: three different actress for three different characters.
1. Severe nurse is played by Ingrid Torrance.
2. The Queen of Hearts is played by Jennifer Koenig
3. Cora, Regina’s mother, is played by Barbara Hershey. 
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy