How can I set up PC gaming for someone who needs to lie flat in bed?

A small overbed table or lap desk could hold the keyboard and mouse, provided it doesn't press on her and she can reach both comfortably while flat. A compact keyboard would leave more room for the mouse.

Check the dimensions before buying. A lot of laptop trays are too narrow for a separate mouse, and a tray that works when sitting up may be awkward when lying down. Secondhand or homemade might be the best bet for that budget.

Consider a trackball instead of a regular mouse. It stays in one place, so she wouldn't need room to move her whole arm around. Pair it with a wireless keyboard positioned wherever her hands can rest comfortably.

There's a learning curve, and it won't suit every game or every hand position. It may be worth trying a borrowed or used one before spending much on it.

For games that support it, a controller might be the simplest thing to try first. She could hold it in a comfortable position without needing a mouse surface at all.

Controller mapping software can also map mouse movements to a controller for games that need them. A small keyboard or phone-based PC control tool could help with typing and menus, though neither is a perfect substitute for a full keyboard.

Before buying a table, work out where the screen can go while she's looking straight up. The arm you have may work, but check its reach and the weight it supports. A bedside cabinet also needs to be stable enough for the arm and monitor, especially with the arm extended.

A screen at the foot of the bed and prism glasses are another idea to explore, though comfort and cost will vary. Whatever you use, avoid a setup that could fall onto her.

If the usual controls are still uncomfortable, adaptive controllers with separate buttons and joysticks are an option for PC gaming. They're likely beyond the current budget, but they could be worth researching if a basic setup doesn't work for her.