They'll just steadily carve slices away from the bottom up.
Which means we'll end up with just her stupid fat head in a jar, dribbling utter shite about the fabulous life it's leading as it demands the butler move it to a warm spot, drape a Tooooorrrd tarpaulin around it, then get a wiggle on because it's hangry and someone needs to drop cheeseburgers into the jar stat.
And that, gorls, is how Albert will lose weight. And she'll be smug as fuck about it.
"Ah'm thinkeeeeen abaht geteeeen a new joar type sicha-ayshun. They had these ones in Wormart that were LIDUHrully larf, just saHOOpercyoot and Ah can put mah choker round the base and these amazeeeeeen bows can go on top ..... "
Wonder if sentient heads can size themselves out of jars? Distant cries of "push, Becky, gnnnHhhhrrrr.....PUSH...god, Destiny could do this, why can't you do ANYTHEEEEN like she could....PUSHAAAAARGNNNNARGGH" are met with the awe-inspiring sight of Necky trying to squoosh her beloved's huge head into the biggest jar she could find cos after this, the only option is the dreaded bucket. And everyone knows the bucket is the equivalent of the mummuu and our dainty gorl is NOT going there booboo...