How do I handle a mother in law who keeps asking for money?

I'm a newlywed. My mother-in-law keeps asking us for money. While we can spare it, it's preventing us from getting out of our student loan debt. My husband and I share a 10 year old car between the two of us while she has a really nice one. She has no job and no money. If we don't help her out, she might expect to live with us (she has mentioned that before) and I don't think I could bare it. I don't mean to sound selfish, but I'm a newlywed and I'm very clean while she is very messy, etc. etc. My husband gave up a masters program to help her out financially. I know she is capable of getting a job. She just chooses not to. My husband is worried that she'll end up on the street but I feel like her situation is her choice. I have spoken with my husband and he is very understanding about my feelings, but he also feels obligated to help. I just feel like we are enabling it. What do I say to my husband and how do I handle this?