I am worried to death about having enough money to bury my mother. What do you do if there's not enough to take care of her funeral?

Consider cremation. It is FAR cheaper and you could do a memorial service at your house for friends and family.
I don't even have to go to the cemetery to visit with my mom, she's in a beautiful wooden box in my living room. People that visit don't even know what it is, other than something on a shelf, but I know. :)

Be extremely careful with the preplanning contract. Make sure you know exactly what it covers. My mother paid $36 a month for decades for her burial. When I totaled up her payments, it came to about $13,000. When she passed, it cost my husband and me over $7,000. That was the “bare bones” burial. There was no obituary. She and my Dad already had their plots. All they did was arrange for the cremation, and bury her. The headstone (also bare bones) was $5,000. To this day, I really think we were “taken to the cleaners”. I would even go so far as to have a lawyer look it over. My husband and I are considering donating our bodies to a Med School.

We worry about the same for ourselves, but have gone to the funeral home and since money is an issue we wanted quotes on the bare bones type of funeral.
No rental of rooms for visitation and no services. We decided to go with cremation and then have a get together for a 'memorial' for ourselves.

The cost was about $1,000 for a direct cremation with no visitation, no embalming, and no fancy ash holder.
Far better and easier to pay for than a full blown funeral that costs about $10,000.

It all depends on what you want to do for a funeral. It doesn't have to be ultra expensive.