From the link cluciano provided:
Can a grand jury target offer evidence of his or her own?
For the most part, the subject of a grand jury investigation has no right to testify unless subpoenaed, nor any right to compel the grand jury to hear certain witnesses or evidence. Often, however, if a target requests an opportunity to testify, he or she will be permitted by the prosecutor to do so but without a grant of immunity.
The prosecutor may refuse to present evidence submitted by a target. In federal grand juries, exculpatory evidence need not be presented, although in many states exculpatory evidence must be submitted for the grand jury's consideration. Prosecutors have the right in federal grand juries to introduce hearsay and to otherwise utilize evidence that would not be admissible in a regular trial.
What protection does a target have against witnesses lying to the grand jury, or against the use of unconstitutionally obtained evidence?
None. The target's only redress is to challenge the evidence at trial. One of the reasons a witness may assert the Fifth Amendment is that he or she does not know if the prosecutor has presented witnesses who have lied. The witness cannot risk testifying contrary to those witnesses, for fear of being charged with perjury if the prosecutor does not believe his or her testimony
I just don't see where it would be to either side's advantage for her to appear. I'd also like to know if a target DOES appear and testify, would their testimony be allowed in trial or would it provide a basis for appeal in some way (because the attorney isn't allowed to be in the courtroom, present evidence or cross-examine)?