Rosiebelle17 I think I would sit down with her in her own home, or garden, and have a chat. The reason for her garden is you can leave when you are ready.
I would do as Serin suggests.
"I would ask her if she is ok/ has she got some sort of anxiety condition? as she constantly checks up on you, and actually it's making you quite anxious yourself and you cant relax anymore.
If she says yes, you could sign post her to her GP as a better person to help.
If she says no then you could say that you think the world of her but need some space..."
I would talk about respect for privacy and that she needs to be invited to come round. She may feel that that is not how she does things, maybe she would have loved her own mother in law to visit 5 times a day. Maybe talk to her about that but even if she would have loved that, or hated it but it happened, YOU are the mistress of your own home and you are busy with your kids and you need her to respect you.
Then I am afraid if/when she comes round uninvited you simply do not open the door to her.
I know everyone says it's your husband's place to tell her, and maybe it is, but he hasn't done that. And many times I've let other people do things that they did badly, and I wished I had simply done it myself.
You do not like her presence so you have nothing to lose, she has everything to lose here and so she needs to respect you.