Ever had critique partners question a sentence like this?
The waiter that spilled coffee on my new dress offered to pay the dry-cleaning bill.
Some will say you shouldn’t use “that” for a person. But Garner’s Modern American Usage and other expert sources say it’s acceptable.
Are your critique partners wrong?
The sample sentence is grammatically correct. So if your crit partners are under the impression that who is the only correct relative pronoun to use for humans, then yes, they’re wrong. Grammatically, either who or that may be used.
But the sample sentence is still potentially off-putting. Calling a human being that does rub some people the wrong way. So your crit partners may just be expressing their opinion.
Whether to use that or who in a case like this is entirely a matter of personal preference. For the record, I recommend who for humans, because I think it’s more personable. But that is an opinion of style, not a rule of grammar.