I agree that she is behaving like a mother-in-law.
I also agree that there is no reason for you to put up with her unreasonable behaviour - especially in your own home.
You haven't lost perspective. The events you describe don't seem too bad as a one-off, but I'm sure it's just one in a long line of annoyances, and you do need to sort it out, imo.
From experience I know that if you don't make a stand with people who have these sorts of personalities, they will get worse.
My MIL is a very abrupt, rude and critical person. She can give it out, but can't take it. She will cry and moan and sulk and whimper when challenged, so everyone let her get away with it.
Until I came along!
I don't see why someone should be allowed to ride roughshod over the feelings of everyone else, just because they react badly when they are told they are being unreasonable.
Deal with her as if she is a toddler.
Clearly set the boundaries of how you would like her to behave. Do it calmly, and use humour if possible. (use puppets, a tambourine and a glockenspiel if you have to, but make it clear as day!)
So maybe say "thank you for taking an interest in DS's health, but he is absolutely fine. I would prefer it if you didn't poke and prod him, as I will know if he is ill. I'm neurotic enough without you making it worse" (cue laughter! ).
If she ignores you, then say:
"Do you remember that chat we had about this?"
Graduating to:
"Well, it is important to me, so I'm going to have to ask you again".
Go on to timeouts if necessary, where she can't visit until she promises to back off.
So she has a tantrum - she's a grown woman, she'll get over it!
I understand that she feels very protective of your DH. This is where he comes in.
He needs to make it blatantly clear that you and your child are his first priority. If she is rude to you, he needs to firmly tell her that her behaviour is unacceptable.
You both need to stand together on this, and have clear boundaries on the sort of behaviour you will take from her. (See, united front, think toddlers! )
(Can you tell we've had a similar scenario in our family? )
Your DH is the key. Until he proves that he doesn't need her to be his mother figure anymore, and stands up to her, your attempts to modify her behaviour won't be successful.
Good luck - and stand firm.