How far is your mil travelling? And how long in advance of eating?
My mother always made her traditional stuffing when doing Christmas lunch because we all loved it. When my gran - her mil - came she was very surprised that my mum hadn't made her traditional stuffing as fir her it wasn't Christmas without it - however my gran and grandad were the only ones that ate it and enjoyed it (the rest of us had to have a token spoonful to force down).
So she would make it at her house in a dish, cook it, put foil over the top, wrap it in a newspaper and then wrap the whole lot in a large towel.
They would the come straight over to us and it would stay wrapped up like that in a warm place until needed and it would be fine. They would arrive maybe 30-60 minutes before eating usually.
If they were going to my aunt's for Christmas lunch she would do the same but as they lived further away she would sit the hot pan on a hot water bottle between the paper and towel layers to provide extra warmth and it would last with no problems.
Although there's probably some food safety expert spinning about this nobody ever got food poisoning (it ws a meat based stuffing) and was something considered squire normal - when my gran was growing up it was very common in the village she lived in to take your meat down to the bakehouse to cook, popping down half an hour before the end to pour the Yorkshire pudding batter around the meat, then bringing it home once it was cooked, wrapped in newspaper albeit with a bit of greaseproof paper on top instead of foil.
If your mil did this, and took the turkey tray out of her oven, straight onto the foil which was sitting on the newspaper which was sitting on the towel then wrapped up within moments of it coming out of the oven it would stay warm for a long time and wouldn't need to go into the oven when it got to your house - or if it did, a minute in the microwave would be all it needed and it wouldn't suffer from feeling like it had bees microwaved.
I can see why your dh would get upset - I'm not veggie but I don't like fish and occasionally I've been places at mil's where she has cooked a meat dish and a fish dish in the oven at the same time. And the meat dish is horrid because it has an air of fishiness about it that spoils the taste of the meat. And she just doesn't notice it as she likes fish and meat and is having both on her plate anyway. But for me - tastes vile. I'm sure that a veggie would similarly taste the turkey-ness on the veggies cooked in the same oven.