My dad (age 81) underwent a whipple on May 31st and had to go back into emergency surgery a few days later because of a complication with the feeding tube. He was in ICU for 29 days following surgery. Because the feeding tube was removed, he was given TPN (by vein) and quickly became very malnourished. Because of that, it has slowed his healing considerably. When the staples were removed, the wound quickly reopened and he had a lot of necrotic (dead) tissue beneath the surface. He continues to receive wound care treatment and I have to clean and pack the wound twice a day (he has two fairly large "holes" in his abdomen).
My dad also has a decreased appetite, which I understand is typical following this procedure.
Encourage your mom to eat several small meals a day (high in protein - according to one of my dad's docs) instead of three larger meals, which will in turn help her heal more quickly.
I also understand depression is commonly associated with PC and following whipple. Antidepressants may help - or possibly find a support group in your area for not only your mom to attend but also your family.