Ok, not really MIL, but my partner's mum. We've lived together for 6 months.
DP doesn't bother getting his mum anything for mother's day. That's his choice and I'm sure she is used to the arrangement and doesn't expect anything. They have a good relationship but DP doesn't really buy into all the commercial "hallmark holidays".
Since moving in with DP and away from my support network, 'PIL' have helped me with childcare, car trouble, make us lovely meals every sunday, and are just generally wonderful.
I don't go daft on my own mum for mother's day either, just a bunch of flowers and a card, sometimes we go for lunch.
Would it be odd if I gave DPs mum some flowers too? Maybe without a card if that might be a bit much?