Listeria is a bug that does still grow in the fridge (one of the only ones I think). So even if the meats been refridgerated, wouldn't it still be a no no?

I think the best thing to do is to ring MIL and explain that you are not comfortable eating the meat cold (and why) and see what she says. Maybe she can do one of the meats on the day for you. Or if you think it would go down better, ask DH to ring her for you.