She got her buck teeth fixed after she hooked up with bill
She seems to realize her doctored spread of teeth is physically her best feature, so whenever she goes into public mode, she spreads her mouth wide open into a dental panorama, wide enough to charm any dentist.
Opening wide is easier than talking when you’ve gotten an unpredictable, uncontrollable cough. Maybe her frequent hacking cough comes from her gapingly letting in flies, gnats, and small debris.