M.D.
I would tell her to keep very close track of her blood pressures (multiple times per day) if she's worried about pre-e. Also - the other women are right - if the swelling never subsides even with complete rest (like overnight), or it is present all over the body, not just the feet/ankles, then definitely get checked out. Some other warning signs of pre-e are visual disturbances (flashy lights in your line of vision, black spots, gray haze, etc), severe headaches that don't go away with rest, quiet, dark and Tylenol, and a pain under the ribcage. If the last three signs are noticed, the person should call their dr IMMEDIATELY.
I had pre-eclampsia from week 36 on, and it was missed until I had labored for 24 hours at 41.5 weeks. My blood pressures were never higher than "borderline" (140/80) until my labor. I also wasn't spilling more than trace amounts of protein, nor did I have the severe symptoms (headache, pain, and visual).
For more information about pre-eclampsia, check out www.preeclampsia.org