How do I fix this phone if it was water damaged?

A lot of the time when it sits this long, the damage is terminal. What you can do is try and take the motherboard out and soak it in 91-99% IPA or put the board in an ultrasonic cleaner and see what can be done. Follow the guides here to take it apart: Motorola Razr V3. Some tools of the era are BitPim and Motorola Phone Tools -- get the Moto tool from archive sites, it was pulled when Lenovo bought Motorola out. You NEED A XP MACHINE, or a VM. Don't expect these tools to work on a modern PC - get a XP era PC, slap a Samsung SSD or one with known SATA II support, load XP Pro SP3 on it and then run the tool. They are cheap when the HD is missing and there is no OS. You pick if you want a classic ThinkPad like the T400 or older Latitude. There is a 100% chance the CMOS cell will be dead, so it will yell at you about that, press the continue key and move on. There are other late era Dells and such with XP drivers as well with SATA III support - look at the driver page and see but a LOT of them from Dell and others kept XP driver support up until the end for XP.

Use this to clean the liquid damage: iPhone Liquid Damage Repair

If your mom put a PIN on it, these phones have a backdoor: I do not remember the exact key off the top of my head (if I worked with it I'd know) but if you press the menu button it asks for a 6 digit security code. Enter 000000 - nobody ever changed it. Do not change it if this works either as the code cannot be easily reset without flashing the stock ROM back on by holding * and # and using a Windows XP laptop and a tool of the era. Not fun to do now, as most of them need to be cracked to run, or you need to buy a laptop from the era with credits and program installed at a high markup.