Probably doesn't want to cross those streams while she's still working there. Maybe after the series ends.
I wonder if there is a legal reason she doesn't do it. Anybody can do a lewd cosplay of Yang without getting into trouble but since she's the actual voice actress that might prevent her from doing so.
Lilmrpimp Honestly, you're probably right. There's almost certainly something in the contract about her using the character outside of official RT media.