Why should she thank someone for purposely ignoring what she said?!
It would be different if MIL had bought it as a gift without knowing OP’s views.
MIL mentioned she was thinking of buying a tricycle for the child.
My MIL mentioned that she wanted to buy my 11 month old baby a tricycle during a stroll in the park. I expressed safety concerns due to my own past experiences as child (I had a bad accident on a tricycle when I was a toddler). I let her know that me and my husband would need to look at tricycle reviews and their level of safety to choose the most appropriate one and that we won’t be able use it until 18 months.
OP was clear on her thoughts about this.
MIL knowing this does it anyway and tells OP and OP reiterates what she had told MIL in the first discussion.
The day before his 1 st birthday my MIL tells us that she has bought his birthday present and it’s a tricycle. I replied that we had talked about this and my MIL shucked. (OP meant to say chuckled)*
MIL then proceeds to gift it anyway despite OP twice expressing her views.
The only one causing issue here is MIL for going against what she was told.
If MIL had bought this before knowing OP and her son’s views, she could have held onto the tricycle and gifted it for his second birthday or just returned it and bought another gift. It is not like the tricycle is a must have toy and we don’t even know if the child can actually walk yet or that OP and her DH have space for it.