I really would not suggest going down this method of trying to get tensorflow-gpu into Slicer 4.8.1. This will ultimately require you to build Slicer 4.8.1 from source and also tensorflow-GPU from source, but even then there is likely lacking support for a version that can be built with Visual Studio 2013 as would be required. I believe the latest tensorflow is also Python 3 only as most packages have dropped python 2 support since it went EOL finally on January 1st 2020. So even then you wouldn’t be able to use the current tensorflow in anything other than Slicer 4.11 which uses Python 3.
Instead your effort is best worthwhile changing your logic to use a different event if you are waiting for the ReceiveEvent for OpenIGTLinkIF to be restored.
Slicer 4.11 preview uses Python 3 with modern compilers so there shouldn’t be any issue installing tensorflow-gpu. The OpenIGTLinkIF module is available within the SlicerOpenIGTLink extension if you would like to check out the latest code.