change comes from within.
sure, positive and negative feedback influences our actions and decisions, but self-growth/development is an inside job.
some of the tactics described in the thread, e.g., withholding sex, dropping clues, etc., may help get you through the midterm (by influencing her to get her shit together) but it won't help you graduate (ultimately have a fulfilling relationship with the sexy woman you fell in love with).
ask her how she feels? mention the frequent naps and low-energy -- do not point out the weight gain or unkept appearance. let her know you want to make sure she's okay. listen to what she says and doesn't say (e.g. "I hate my job.. My family is driving me nuts...I'm failing apart...I'm gaining weight...can't fit my clothes...my hair is a mess...OR I feel so happy and comfortable now...I'm finally able to be myself...I'm finally able to rest after years of running...etc).
most women, if not all, want to look good. there's usually a reason why we stop keeping up with our appearance. It may no longer be a priority to us...we feel low or depressed...we may feel we look good without the extra efforts of exercise or hair care...we may be tired of the unwanted attention from men...we may have been abused or have been sexually accosted...etc. etc. If you genuinely love and are committed to her, offer her a supportive environment while SHE figures that out first.
give her some time to sort things out on her own. provide her with a loving and supportive environment that contributes to her (and your!) success (e.g., healthy snacks, initiate but don't guilt-trip exercise-type activities). Revisit the health of your relationship, your feelings and her self growth two months from now.
If no change or she falls off even more, this may be who she is (that's not to say she won't ever change). Love her or leave her alone. You both will be better off.