Not a lawyer, but I had the same visa and this is my understanding:
Once she has "demonstrated immigrant intent" (i.e. applied for a green card) she can remain in the US with no problem, but if she leaves and tries to re-enter on her F1 visa she can be denied entry. Because it is a strictly non-immigrant visa, if they think you intend to immigrate you can be turned back at the border.
However if she gets Advance Parole (which is part of the green card process) before leaving the US she can use that to re-enter if necessary.
She should talk to her school's international office and if necessary a lawyer if she has any questions.
Once she has "demonstrated immigrant intent" (i.e. applied for a green card) she can remain in the US with no problem, but if she leaves and tries to re-enter on her F1 visa she can be denied entry. Because it is a strictly non-immigrant visa, if they think you intend to immigrate you can be turned back at the border.
However if she gets Advance Parole (which is part of the green card process) before leaving the US she can use that to re-enter if necessary.
She should talk to her school's international office and if necessary a lawyer if she has any questions.