Meh..... show me a 3 yo who doesn't chuck tanties.
I think you could gently point out to your mother that there isn't much point in comparing the behaviour of a 3 year old and a 3 month old. You can deal with the 3 yo issues in 3 years.
If you don't see the point in changing because you're all happy why not just say so.

TBH, my reaction to the rod-for-your-backers does depend on thier motivation. My aunt was visting last week and she's a dear old person who only wants what's best for me. She said that letting your babies get in the habit of sleeping with you can be awful because you never get a good night's sleep. She didn't say this to put down my parenting or upset me but just because she genuinley wants me to sleep well. There was no way I could have responded nastily to her, especially since I remember jumping into her bed as a child lol. She just wanted to share her experience and wisdom and since she's raised 2 well balanced happy adults I think she's worth listening to even though I won't always agree.