Who’s debt? Mom’s or yours?
Note that you can’t borrow more than $27K total as an undergrad w/o a cosigner (see https://studentaid.gov/understand-aid/types/loans/subsidized-unsubsidized_ So even more important, is mom’s number from a FA evaluation or her guess? If the school says your family can afford full pay but mom can’t swing it w/o loans then Fed loans are off the table and you will only be able to get private loans with a cosigner.
The difference between $20K and $40K is big! I could possibly justify $20K but not $40K. The thing is you don’t know what the future looks like. If you land a $50K/yr job out of college then the payment on $40K of debt may not look so bad. If, like many students, you need to start with an unpaid internship or lowly paid entry job after college then you will either be unhappy for quite a while, or perhaps even unable to take the position even if it is the best (or only) way to start in your chosen field. Of course that is me; you may be a bigger risk-taker.
I know people that got degrees in Econ from UCSC and they did ok out of college; however they didn’t expect the degree alone to open doors. They hustled to find internships while in college.