You may not find the Reply button in an email after forwarding it. The Reply and Forward options are not directly accessible after forwarding an email, which is a known issue. There is a pending fix for making the features easier to reach. To Reply to or Forward such an email, click on the gray Ellipsis in the top right of an email, and select the appropriate option.
To have more information on how FogBugz manages customer emails, please review this knowledge base article on Handling Incoming Customer Email in FogBugz.