If there is no way change the logic a little to prevent the 2nd flow to trigger immediatly. Depending on what it is doing and if you need the updates from that 2nd flow for the email you are sending, you could add a small delay in the flow, even though it is not ideal or bullet proof, this will at least give some time for the email flow to run. Then you could use some data or maybe also retrieving the emails with the same regarding object and subject and then prevent the duplicate from being created.
If you absolutely need the data from flow 2, you could add a delay in the email flow and check if the value you expect has changed already changed.
All this is especulation on how those 2 flows are related to each other and the actions and times in each flow. If that doesn't solve the issue. You could post more details to try to see what other options someone could think of.