Hey there Rachel1,
I'm sorry to hear you are unable to reinstall your app! I can imagine this has been quite the headache for you, so I'd be happy to help out. Now, is this an app you installed on the Chromecast with Google TV, or on your mobile device? Either way, if you find the app on Google Play while logged into your Google account, Google Play should tell you what devices you own that the app is available on. Give that a try, and see if the app is available to install.
I look forward to your response, and if you have any other questions or concerns for me, please let me know!