A green card is NOT a substitute for a visit visa. She needs to move to the US to live. She may visit elsewhere. If she does not intend to live in the US, she should give up the green card and obtain a visit visa. If it is believed she is not living in the US, the GC can be revoked and she can be denied entry at the border.
Note: You have admitted on a public forum that she is intentionally violating the rules governing the opportunity she was given.

