Could be one of many things. But a couple of easy things to check to get things rolling:

1) Remove the body spray heads. They should be threaded on to a short nipple, a couple of inches long. One end of the nipple threads into the spray head, the other end of the nipple threads into a union in the wall. Check for grit or solder bits inside the head. Clean any mineral deposits away.

While the body spray heads are off, may as well check the flow of the plumbing behind the walls. If the nipple came out of the wall union when you took the spray head off the wall, remove the nipple from the body spray head and thread it back into the union inside the wall. Turn the water on and see how well water flows out of the nipples. Hot, cold, medium temp.

2) Your valve versus her valve. You could remove your shower head and her shower head. Unthread them from their respective shower arms.

Run your valve wide open, see how many seconds it takes for the flow out of the shower arm to fill up a drywall bucket. Or any bucket. Repeat with her setup.

If her's is slower, it could be a problem with her valve. Could be debris.

Sometimes it's a partially closed stop. I never figured out how stops move, but sometimes they do. If your valve has stops, remove the valve trim and exercise the stops. Open them, close them, then obviously leave them open.

A starting point. Have fun!