Unfavorable cervix means her doctor is NOT supportive AT ALL!! That's what it means....
Anyway - yes of course she could go into labor at any moment or weeks from now. And her cervix doesn't speak English and won't tell us when...hehe. Even an "unfavorable" cervix can go into labor soon.
MANY OB's don't believe that a VBAC should have a vaginal birth after 40 weeks pregnant for fear that they will have a rupture. The risk of rupture is very slight but they use this approx. 1% risk number to scare women out of the vaginal birth.
As the doula it is your job to "inform" your client the best you can on things her doctor isn't telling her such as her true risks for complications if she waits to labor AND her true risks of surgery if she chooses to have the cesarean. She needs to make the choice. Unfortunately many women who choose OB's get scared to death by them and give in. That is why the information you can provide is so important to her.
Also if she does go into labor and try for a vaginal birth then she will likely have to face a ton of interventions at this hospital which could make the likelyhood of her success less. When I have a VBAC I generally talk with them beforehand and see if they are comfortable staying home as long as possible in labor and if they are we stay! If they go too early they get stuck with IV's and monitors and get trapped in a triage room and more....and IMO it is even more important for a VBAC Mom to avoid all this than a first time Mom. They can get dejavue if their first birth went south in a hospital - they can get scared and sometimes they can be pressured by staff to do things they originally wanted to avoid.
Well my muchkin doesn't want me to type anymore apparently because he is wailing... have to go! I wish your Momma all the best!