If Wendy drowns with Abigail Summoned and over water then Abigail stays summoned (ie. doesn't revert to a flower).
If Wendy revives reasonably close then Abigail can be collected simply by travelling to the point of your death. However if Wendy revives along way away and takes a few days to return to collect gear then Abigail or her flower are nowhere to be found. (It's possible she is trying to journey back to Wendy as you do seem to hear her occasionally, but I stayed in the area for over ten days before I died without away sign of her).
1. Start a game a Wendy. 2. Summon Abigail. 3. Use a touch Stone. 4. Sail along way away from the touch stone (to the opposite side of the map). 5. Let you boat break and drown. 6. Revive at touch stone. 7. Gather resources and build a new boat. 8. Wait a few days - ie. give Abigail a few days to leave the area of your death 8. Sail to your drowning point