Unfortunately the thing that would help most would be a screenshot of the email app when composing a mail. If we could see what the app looks like we'd have a chance of spotting and pointing out the "send" button. Bear in mind that if this is a Lenovo email app most of us won't have seen the app ourselves.

If the app is really problematic the alternative is to find an app that works better for her and use that. There is nothing special about the apps that come pre-installed on a device, they are just whatever the manufacturer chose to include (and app design is not always a hardware manufacturer's strength).

 

Generally, a paper airplane looking icon is the send button for the e-mail apps that I have used (not many).