I agree with you that it would have been better writing to use alumna. I’m only suggesting that there is a school of thought on the usage that would have her use the male form when referring to a pool of men and women in this context. And, there could further be a case made that she was talking about the circumstance of her being an alum generally, rather than anything specific to her being a female alum, to prompt the use of ‘alumnus’. The thing is incredibly poorly written, reasoned and predicated overall, so you and I are at best disputing a fine thread—when her outfit overall is afire.
“I agree with you that it would have been better writing to use alumna. I’m only suggesting...”
You two. Get a room or something.