What are appropriate expectations of family who babysit?

I’m a new mum and don’t have any friends/family my age who have kids so I thought I would ask here.

We very occasionally have my MIL babysit our 5 month old for us. We had issues with her overfeeding the baby in the past which ended up causing severe stomach upset (my baby has reflux).

We ended up explaining that he can’t be fed that much so quickly and let her know the max amount of food he can receive. She now seems to understand this which has been a huge relief. But unfortunately when we tell my MIL other things she tends to make her own decisions on things without consulting us even though we have explicitly explained why it needs to be done a certain way.

So I guess that leads into the question, how many instructions are too many? I know there is probably no clear answer but I just don’t really have any context because I don’t know anyone else with kids and I don’t know what’s normal.

I am so so grateful with my MIL for babysitting for us and so I’m concerned that we are just loading her up with too much info.

Just for an example, we asked to make sure that for his final nap of the day to not let him sleep past 5pm because otherwise it impacts his bedtime and his night sleep. And we told her we would be home at 6pm. She ended up letting him sleep until 5:55pm.

Is it best just to let babysitters do their own thing or is it best to still try and get them to follow a vague schedule of things??