but did she do something illegal?
If a straw purchase, I would charge her with murder.
Yes, she did. If you represent yourself as the buyer, but you are actually buying them for someone else, thats a crime.
Things that can demonstrate that, are things like proof that she knew of his criminial background and that he could not pass a background check. Evidence that he provided the money for the guns. (ie,,say he let her use his credit card at the gun store)
Evidence from his computer, say he sent her an email naming the exact models to buy for him and that he will pay her cash plus a fee when she delivers them.
Say there are phone records where she sent him a text message saying “i got the guns you wanted, meet me at your place at 2pm”.
Maybe some agent knocked on her door and asked about the rifle she bought. And she answered that she only bought it for her neighbor but never meant it to be hers.
There are many ways a straw purchaser can screw themselves.
Never underestimate brazen stupidity.