If the swelling appears to be water retention, then it's probably edema. This indicates that she doesn't drink enough water (as does the need for metformin, although no one in the medical profession will acknowledge this).
It won't hurt anything to try this, so have her increase her water intake to approximately 2 quarts (eight 8-ounce glasses) per day and decrease her salt intake and see if the swelling goes down. If it does, she should thin increase her salt intake just enough to balance with the water intake (this is a trial and error thing).
If this helps, she can maintain it by staying properly hydrated.
As to the metformin usage, this won't necessarily fix that, since diabetes is a little more complicated. But with the increased salt intake (once she increases it again), it should help regulate the blood sugar and her need for metformin may decrease so that she can be taken off of it.