HELP! I got my mom’s keys locked inside her car and know I can’t open the door?

There are a few things you can do.  For one thing, there should be a trunk release somewhere near the driver's seat.  If the doors are locked too, maybe she has another set of keys.  If you have AAA, they will come out and unlock it for free.  I would only call a locksmith as a last resort, since that will by far be the most expensive (except for breaking a window and replacing it).

If the other doors re open look in the glove box for a trunk opener button.
Before getting an expensive locksmith I'd find the title and take it to the dealer parts department and have a cheap key cut that will just open the trunk.
You need the title to prove you own the vehicle and they use the VIN in their key machine that uses the VIN to program the key to be cut.
Probably under $30.

It might help to know what kind of car it is - some are surprisingly easy to break into (some disturbingly so - like the 944 Porsche where taking two screws out of the license plate light allows you to stick a screwdriver in the hole to pop the hatchback).

You failed to mention if the car itself is locked,  or if it's just the keys in the trunk. Some cars will have a trunk release under the dash, in the glove compartment, etc., and some have the ability to get into the trunk from the back seat (or at least reach in to get the keys out - hopefully without destroying the interior/upholstery).

A locksmith is going to run you a few bucks, so I would definitely spend a few minutes online looking up the particular make/model (or post it on here) and see what options you have.

Watch a few youtubes on opening locked car doors.

Call police. In some areas they will assist but they are not responsible for damage.

You will need a small wedge and a metal clothes hanger. Gently tap the small end of a wood or plastic wedge in/at the bottom of a car window on the metal door. This will open a narrow space at the top of the window. Straighten the wire coat hanger or locate a thin piece of long sturdy metal to push the unlock button for the door. If no button then make a hook on the end of the coat hanger wire an slide it down the inside of the glass to feel for the lock release or make a loop and pull up the lock component. This may take some time to do. If you become frustrated, take a time out.
Or ask your mom if she has a spare key.
If the doors are already open, take out the back seat to access the trunk.