This has nothing to do with the Marshal. If you have a written agreement that says in case of abandonment you can dispose, you're sitting pretty - except how long is it before something's abandoned? Do you not have any way to reach the person? Facebook, text message, twitter, email, nothing? If you can document your bona fide attempts, I think another month is sufficient.
Are there valueables? Large things that take up space? Small stuff, like photos, jewelry, etc., you might...
Life estates don't shield people from creditors. Any judgments against brother that's running from bills will have to be paid from proceeds of any sale or partition action, so you're in a bad spot. And, if he wants his costs back, how are you supposed to do that without his bill collectors attacking his money? Cash under the table?
Sit with a local attorney to outline your rights & potential remedies.
There is no quick solution. You will need to evict her, and like it or not, an attorney is necessary in order to do it properly and to save you time and money in the long-run. The only alternative I see is to offer her cash to leave - which may cost you less than an eviction. Good luck.