Spilled water on mac

She should be able to recover her files from a backup made before the accident.

If there are no backups, then It depends on the exact model of the Mac and whether the internal drive is removable, plus how much water made it inside and where it made contact on the board. Basically almost any USB-C Mac it will be nearly impossible to recover any data, although you can try contacting a professional data recovery service such as Drive Savers to see if they can recover the data. With older Macs with removable drives, many times the drive will survive...again it depends on what the water damaged inside the laptop.

People should always have frequent & regular backups of their computer and all external media (including the cloud) which contains important & unique data. There are a lot more ways to lose data with the USB-C Macs than ever before, plus most SSDs (even brand new SSDs) fail without any warning signs as do some Logic Boards (USB-C Macs have the SSDs integrated into the Logic Board and the data is hardware encrypted...meaning the Logic Board must be working along with the security enclave even to begin to be able to access any data). Plus it is impossible to recover accidentally deleted data from an SSD after the Trash has been emptied due to how SSDs work.

Waiting until something goes wrong to worry about your data will usually result in lost data, or a very expensive & stressful data recovery process. The cost of an external drive (or two is better) is well worth the money to minimize the chances of data loss. Apple includes the Time Machine software for free with macOS. The more important the data, the more backups there should be, with one possibly being stored at a different physical location. Unfortunately most people tend to learn this lesson the hard way.