The sentence the judge handed down is 15 years in prison at minimum. “To life” implies no maximum limit to it.
After the 15 years is up, she can apply for parole, and her case will go to a parole board, where they will evaluate whether she has served enough time in prison and now shows remorse, as well as any indication she can integrate back into society. (I think the victim’s families can also offer input if they want). If the board agrees, they may grant her parole, and let her leave prison, but with conditions attached that could send her back if she violates them. And with no maximum to the term, even if she were let out she can be subject to those conditions for the rest of her life.
If the parole board declines her application, she will be able to apply again in a few years. Even if she is a model citizen in prison, the board would be within its rights to say “You need to serve more time to answer for your crimes before we can parole you”. And since there is no maximum to the sentence, they can keep saying that for as long as they want to.