How can I make ahead a stew containing rice. I don't want the rice to absorb the liquid and get gummy.

Panfusine has the right answer. Toast your rice in a little oil or butter before adding it to the stew and this problem will be solved.

Lots of good advice, and I'm keeping that info from chantalemarie!

Once rice gets past a 15 or 20 minute soak in a hot liquid, it will have absorbed all the moisture it can contain. Beyond that, its ends begin to splay, then the rice turns glutinous, then it disintegrates into tiny white granules, which makes for lousy leftovers of chicken and rice soup.

With 25 people depending on you for dinner, I think you should play it safe. Either cook the rice separately from the stew as suggested above, or add the raw rice to the stew no more than 20 minutes before serving time.

try lightly toasting the rice before cooking it

All of the previous advice is good on handling rice---similar to what I do for gumbo. But then there's this other side of me that asks, "what's wrong with gummy?" As in the starch does work to thicken it. That's not a displeasing aspect to me.

I agree with SKK and Soozll. This is how its done in restaurants. We always par cook risotto then spread it on to sheet pans to cool quickly. When we get an order or two we just heat up what we need. Rice could could be steamed briefly to reheat but be sure to wrap it well. Dry heat (oven) would probably be better if it is fully cooked. Maybe the oven in foil with a little fat to keep it from drying out, or reheated in batches in a skillet.

Cook them separately and keep them separate. Scoop the rice into the bowl and serve the stew over it. They can both be warmed separately as well and served as before.

How about cooking the rice separately and adding it to the rest of the ingredients when you warm the dish up?

Add big chunks of potato and remove them later. It works pretty well.