Why did my ghost shrimp eat my snail?

I feed my ghost shrimp a couple tiny pebbles of goldfish food each day. Yesterday, I seen the snail moving around in the bowl as usual. This morning I looked in the bowl and I seen the empty snail shell, and my ghost shrimp's stomache is now black. (It's usually tan like the goldfish food). His insides are black, and the snail is black, so I'm pretty sure she ate it. This totally freaked me out! Maybe I'm not feeding her enough? I've had them together for a few months and they never hurt each other. What do you suggest I do? Is it okay for her to be alone like this? She has now ate her only companion, haha!