It only voids the process if she travels after she has filed an I-485 application and has not received an advance parole travel document before traveling. But

It only voids the process if she travels after she has filed an I-485 application and has not received an advance parole travel document before traveling. But traveling on an F-1 visa after an I-140 has been filed, while it doesn't result in cancellation of the I-140 petition, is also risky. Definitely, consult with someone before you or she commence the green card process.