I would

[Louis VI the Fat]

http://www.dailymail.co.uk/health/ar...s-16st-on.html

Wait for her and swear to God in heaven that if she doesn't lose sixteen stone you will cave her head in with a sledgehammer.

Or, seeing as how any hammer will probably only bounce off of her, take up a sport together, like sledgehammer throwing.

Failing any of that, tell your sister in the UK to lay off the fish and chips and to come back home.