Hi - sorry to hear your sister is suffering. You said her mouth is so dry all the time - I'm assuming this is why she is rinsing and spitting constantly - biotin has a mouthwash that should help - they also have a spritzer that may help, and they have a gum. All designed to help with the lack of saliva. And I hear it's available at Walmart.

Otherwise every bit of advice these guys have given you is gold push her Drs. To find out why she can't swallow and it sounds like she does need some counselling. My thoughts and prayers are with you... Take care