My mother in law wants to go trick or treating with us for our first Halloween 🫠

I think the problem here is that she doesn't help enough for you. Why won't you say that to her? Having an honest and respectful conversation.
To me trick or treat is actually more funny with more people then just 2 persons. I understand where you are coming from. I just think that the problem is not there.

we had this talk whenever I was diagnosed with postpartum depression. My husband asked her to come help since she only works 3 days a week and she said she would but she never did. Every time she came to help was because I called asking. That got me tired and I stopped asking for help completely and she now comes over maybe once a week for 30 minutes, play with my son and go home 🤷🏻‍♀️

I don’t think the problem is the trick or treat itself either. I feel like being part of my family is a privilege that she doesn’t make any efforts to have.

Yeah I understand. Nowadays, lots of grandparents are very shitty ones... That's very hard to deal with that.

Is it that she’s owed? She doesn’t help? Partner doesn’t want conflict? Or is it that you really would like to have some space to start your own traditions?
Think a bit about which is most important and maybe that will help clarify what you need to do.
With my first it was big we made our own traditions. Now it’s just important we do what we want for our family. I wouldn’t care personally if anyone in our family joined in trick or treating. But if there’s tension already it can sour the holiday.

Sounds similar to my daughter’s great grandmother don’t get confused by the great part she’s only 63. She always says she will come down but has only came to my house 3x and my daughters almost 2. She’s down the road all the time but chooses not to pop in. But expects me to pay 60-80 to travel to her house and back to mine very often and I just can’t afford to travel so far but she drives. She’s insane. I honestly would tell her if you say you will help then I expect you to help I don’t go back on my words and I don’t expect you to either but you have and me and your son have been through such a hard time yet you haven’t helped as much as you said you would if any at all. If you can’t do something so simple I personally don’t want you at our family events because what’s the point having a once in a blue moon baby sitter at family invents act like family and maybe you can be invited that would be my response may sound rude but honestly I personally wouldn’t care

The only tradition Im creating for Halloween is all of us in costumes and I wouldn’t mind she coming if she did enough to be part of that moment!

I had a similar issue with my own parents, I found actually giving them a set time/day to come around every week to help worked. It still wasn't easy then as they initially just watch me parent, I would then find excuses to be out the room then gradually out the house to build up the amounts they were looking after him "solo".

Thats what we tried in the beginning 🫠 I told her she could come anyday between 1pm and 5pm and to just let me know the night before. We started having problems because she smokes weed, would get high too early and sleep the day away or she would come high to my house. It’s not like she is a bad person but sometimes I feel like she thinks she is still a teenager since she is an empty nester. And Im totally cool with that since nobody has obligation to help me raise my son but there is no way I can just pretend she deserves the grandma title. Its a mess!

Yeah I get it, it is so frustrating. It would be really helpful to have that help though and also perform the role she's been gifted with.

Is it worth your partner speaking to her and voicing your frustrations? She might not realise how much of a pain she's being.