OP, no one has been rude to you at all, people have stated they disagree and why and how your previous history shows that overall your mother in law is nice, the only actual "issue" you have with her is her buying your children clothing - which isn't really an issue considering nothing else in her behaviour suggests she's an awful controlling person.
I'm sorry to hear you are lonely and that you have mental health issues, but no one is controlling you, and your mother in law buying these items does not mean she is either. Perhaps it's issues you've mentioned with your own mother in the past that you are now projecting on to your partner's mother.
I have read many of your threads in the past as I often do read and not comment, but I really wanted to say something today. I think you do need to seek professional help as you do appear to have control issues and unresolved issues from your past.
I do hope things get better for you, but honestly what your mother in law is doing is what most grandparents do, it can only be offensive if you look to take offence.
You can begin to make your life slightly easier by actually being more appreciative of what she does and not taking offence, if she does buy something you feel your children do not need or you don't like - so be it. Children often receive gifts they do not need, but it's a way those that love them show their love.
Also, as others have said, children's shoes should be comfortable from the get-go as their feet are so delicate, so perhaps there is an issue that your mother in law has noticed and is helping with. The worst case scenario is is that your son has two pairs of shoes.. hardly anything to get worked up over.
Look after your health and yourself, these non-issues are not worth getting worked up over.