I have a found at times air does enter the lower half of my suit but I can get round this by just pushing my legs down (vertical) and then the air rises into the suit. Our club taught us to dive at an angle just off horizontal so air stayes in the main body of the suit.
My partner dives with ankle weights which she hates and says don't work. A guy in the LDS said she might try tighter fins. She has a pair of Mares fins in a large and they do have a large hole for you foot. I on the other hand have a medium Scuba pro and as they are a tight fit I have managed to get away without weight by monitoring my dive posture and not letting too much air in the lower legs without correcting it. I guess we might just swap and I'll learn to cope with larger fins. (This should be great as they colour coordinate and I get to swap my on Scuba pros for a shiney new set
Sorry Josie
Dave C