If your sister removed RAM from your computer’s motherboard, you can re-attach that. CD-ROMs, hard drives, and the like can be reconnected. Cards are designed to be taken in-and-out of your computer — graphics cards, ethernet cards, sounds cards, USB cards, etc. And your motherboard’s battery can also be taken in-and-out. Definitions for all of the above terms can be found online.

If any other part of your motherboard was damaged, a computer hardware expert will need to conduct the repair. Be aware that such repairs are often expensive, and not always successful.

I strongly recommend that you consider selling your damaged hardware on a site like eBay, in order to fund the purchase of a replacement computer. Many geeks love to purchase damaged hardware, repair it, and sell it for a profit.

Does this help?