Carolyn Hax: Girlfriend makes less money. Should their rent still be 50/50?

Adapted from an online discussion.

Dear Carolyn: My girlfriend of 1.5 years and I plan to move in together when our leases expire. She showed me a breakdown of her monthly finances, and she can’t afford to pay half the rent for a lot of the apartments we were interested in. She volunteered that I have the option of paying more than half the rent because I make more than she does and will save a lot of money by moving out of my current apartment, which is all true.