Don't force your toddler. Toddlers are at the age where they hate following instructions.
Just leave it. She will call you mama eventually. It's not healthy to develop negative feelings due to this issue.
Don't make a big deal out of it. You can constantly refer to yourself as "mama" when answering her so she can link you with the word "mama".
For example, you can say something like, "Yes, Mama is here.", "Would you like to play with Mama?"
Read more