She doesn't need to drop off paperwork, that's what the postal service is for and she should use it. Tell her you're unavailable for such a visit. Since you've already said yes I'd claim illness, be "ill" for weeks, all of you and tell her to put it in the post.
Put your phone on silent overnight so she can't disturb you.
Tell her, literally, to mind her own business about toys or how often you vacuum, when she comments. She won't like it but tough shit, she started the rudeness by commenting and you don't owe rude people politeness. She's not the queen and you don't have to treat her like she is.
She has a right to come in for annual inspection and repairs/maintenance work, that's it. I expect she chooses school holidays because she works term time herself. If it's a short holiday not the summer one just tell her you're unavailable for inspection that week but can accommodate the next week (when DS is back at school). She's being totally unreasonable. If she's working she'll have to take the day off to inspect. You can tell her your son is unwell, every time, if it helps. It's not a lie, he has a permanent condition that affects him.
You'll have to be a bit flexible if something needs doing as an emergency over the summer though. If it's not an urgent repair I'd leave reporting it until he's back at school. For annual maintenance and inspections just bring it forward to before the summer holidays, that will reset the date to a more convenient time for you.