Did your mother report the crime when it happened? Is so, then it's possible that a DNA match could be done, but that is up to the police and prosecutors to follow through on. Your mother would have to take it up with them and find out if they want to do that.
Even if a match was found, many states have a statute of limitations on prosecuting rapes. Your mother would need to know if there is one where you live.
If the crime wasn't reported when it happened, she could report it now, but chances for a successful prosecution are not good even if a match were found. Again, this is something that could be affected by a statute of limitations, and is something that would have to be discussed with the police and prosecutors.
You need to discuss this with your mother and find out if she even wants to re-open all of this. She may not. Ultimately it is her choice and you should respect her decision even if you disagree with it.
I used to care. Now I take a pill for that.