I don't think a woman (or man) has the right to demand that their partner invest precisely the same amount of effort into their appearance as they do; people are different, and you cannot expect someone to adopt a new set of priorities simply because they are the priorities you yourself hold.
However, I think there comes a point when displaying a lack of concern about your appearance indicates a lack of respect and concern for your partner. If you are in a long term, committed, monogamous relationship, one of the things your commitment implies is your intention to provide for the sexual needs of your partner. You should not deprive your partner of the ability to have a sexual relationship with a mate he or she finds attractive.
Using weight gain as an example - gaining a few pounds as you age is natural. Gaining a few more than your spouse can be attributed to acceptable differences in temperament between two people. But if one partner stays trim and the other lets themselves go and becomes massively obese, then I think the fit partner has a right to complain. Wanting to be attracted to your partner does not make you shallow, it makes you human.