My MIL always loved salt. She'd even heavily salt her salad - I'm talking visible crystals from across the table. She's massively overweight so I assumed this was typical fat person behavior. She actually couldn't taste her food anymore because she had early onset Alzheimer's. Worse, no one will make her stop so her blood pressure is through the roof and she's been hospitalized multiple times from sodium buildup in her blood. Apparently, a shitty super salty diet can cause the arteries to narrow and get clogged with salt crystals (so her doctor said but he was probably oversimplifying things). Despite being shitlorded hard by her doctor, she insists that it's not her diet but the weather that's making her ill. It's too late for her but she's part of the reason I became a shitlady and shitlorded my husband into humanity (yes, I married a ham). So, if your bf's mom is eating fucktons of salt, over seasoning foods, or messing with food texture (such as applying copious amounts of cheese to a cheese pizza), she might be losing (or already lost) her sense of taste. That may or may not be dementia related but either way it'll probably only reinforce her ham behavior.