If she gets pardoned, she can be subpoenaed. She'll no longer have 5th Amendment rights against self-incrimination, because she can't incriminate herself for something she's been pardoned over.
She can be hauled before Congress. If she keeps her mouth shut, she'll be charged with obstruction. And if she lies, she'll be charged with lying under oath.
I don’t know this for a fact but I would imagine that Ghislaine would like to get as far away from the United States as she can get—perhaps somewhere out of the reach of our authorities.