In my (British) English, I would always include the ‘it’. This is either a American expression, or possibly an American colloquialism and you would still include the ‘it’ if you were speaking in a more formal manner.
I could be wrong, but “it” in mom’s sentence functions as an “expletive” in the traditional sense of that grammatical novelty. (Not as a metaphor for vulgarity.) For example: “It’s raining.” What’s the “it” in this sentence? “It” is an expletive—a filler word to fill a void in a sentence without adding to the sense—extemporization. Mom’s aversion to anybody populating her room seems like a similar application of “it.”
You can definitely leave out “it,” and you should. It’s sentence clutter and only makes the reader’s task harder.