Prodromal labor is so hard emotionally on the woman and even for those around her. It's like a roller coaster ride that never seems to end!
I agree that it's important to remind the woman that her body is doing something and getting lots of necessary work done in order to birth her baby.
The cervix dilating as we all know just doesn't tell much about where a woman is in labor.
I was at 3cm with my first for over 8 hours of my labor and then within in 20min. progressed to 9 1/2. With my second I was 7cm at the beginning of labor and it still took 5 hours to feel like pushing.
I was providing labor assistance to a woman who was 5cm when she got to the hospital and the nurse told her that she had hours to go! I just didn't believe it because this mother had all the signs of transition...sure enough she had to push a 1/2 hour later and the nurse wouldn't believe us...when she checked her dilation she was 10cm and the nurse panicked because the had told the doctor not to come in yet...the nurse caught the baby!
I teach extensively in my childbirth classes about reaching a plateau in labor where dilation doesn't continue for a while...this is where moms are told that they are 'stuck' or a 'failure to progress', my favorite! But it's quite common to plateau out for a while but that doesn't mean the mom isn't working hard...and most moms once they move past the plateau enter transition and are close to pushing.
I would encourage her to not concentrate on the labor anymore than she needs to. If she's up to it go out to eat, go see a movie, go walk the mall, whatever she may be comfortable doing to get her mind off of it for a while...or at least try to get her mind off of it!
Encourage lots of rest, fluid intake, warm showers/baths to help relaxation.
Avoid lots of VEs (depressing to hear that you're still at the same cm you've been at for hours).
It sounds like you are working with them prenatally to ensure certain things are in order and that's good, but sometimes it's just the way a woman's body needs to labor. I emotional issues play a big part in a labor being slower.
Encourage her to work out any issues she has...it could be about who's with her during labor. Maybe her MIL insists on being there but she really doesn't want her, or perhaps her and her husband have some problems, or she isn't comfortable with her nurse, or she's scared about what kind of mother she'll be. Any emotional hangups can play a big part in what our body does.
Anyway, just my random thoughts.

Blessings!
Amy