I didn't know my mum was moving in with you...
Tell her she's allowed her opinion, but your apartment is your personal space and you like it as it is. If it's not good enough for her, she doesn't have to move in. If it is good enough. then she should shut up with the nasty personal remarks. And they are personal, because you chose the furniture, or at least liked it enough to keep it, so she's basically insulting your taste.
Be blunt, honestly, it's the only thing that sinks in. Talk to her before she moves in, and if she rolls her eyes or acts like you are making a big deal about nothing, don't let her move in. You don't need that kind of negativity about your home.
I'd agree with Willard on this.