I think in this case, only your friend will know what the right way to solve this is.
She'll know how it feels to be with either of them. She'll know who she can trust, who can make her happy and who can make her feel wanted and safe.
Best advice you can give her is to ask herself those questions and don't rush into something for the wrong reasons.

Atleast that's what I can think of! There's not much to go on :-)