components.js

import RelayEnvironmentProvider from 'react-relay/lib/relay-experimental/RelayEnvironmentProvider';
import useLazyLoadQuery from 'react-relay/lib/relay-experimental/useLazyLoadQuery';

// ScreenA
function ScreenA() {
  const { root } = useLazyLoadQuery(ScreenAQuery, null, {
    fetchPolicy: 'store-or-network',
  });
  return (
    <RelayEnvironmentProvider environment={environment}>
      {renderSomeComponent(root)}
    <RelayEnvironmentProvider>
  );
}

// ScreenB
function ScreenB() {
  const { root } = useLazyLoadQuery(ScreenAQuery, null, {
    fetchPolicy: 'store-or-network',
  });
  return (
    <RelayEnvironmentProvider environment={environment}>
      {renderSomeComponent(root)}
    <RelayEnvironmentProvider>
  );
}