Tammy does not want to change. Period. She may say she does but really she doesnt.
Imho Tammy is stuck as a perpetual 11yr old (around the age the grandmother died) who wants what she wants but doesn't want any consequences for her actions. There's always something to blame - her crappy childhood, the mother, the grandma, Amy & Michael, Chris, Covid, etc etc.
As frustrating as it is, no one can make Tammy lose weight if she's not willing to put in the work or sacrifice in any way.