I woudl try booster seat right at the table, and just a few bites on the plate at a time of diffreent pieces....as she takes the last bite of one thing, get excited about putitn gthe next thing on her plate, "Ooooh look, some X for you now!"
Honestly, mealtime = sitting, family, conversation time for us too, so I understand why it's valuable for you to not have her running around. I'd slowly work your way up, in very small increments. I'd extend her sitting by 1 min past when she's "done" the first few days, then 2 min the next few, then 4, etc. etc. until she's sitting the whole meal (or 10-15 min, depending on how fast you eat - we eat fast, so I expected the kids to sit the whole time since we only took 10-15 min to eat and I didn't feel that was asking too much with food and conversation).
Heather, WAHM to DS (01/04) * DD (06/06). Wed to DH(09/97)