You can't represent someone else's tension - it's unconstitutional in any case, and, as Tracey discovered, a terrible idea to try! :-)
You can represent someone else's role, with permission, to process a tension you sense in that role, which is a totally different thing than representing someone else's tension. I think that's what Gabriella was intending to ask about, although there's nothing that allows a role to be "represented by another role", just by another partner. And then they can represent the role just as if they filled it, and process any tensions they actually sense in the role.
There are no rules about how/when that permission is given, so it's up to everyone involved to use their judgment there. I often use this when I'll miss a governance meeting, and I know someone else who will be present has a good sense of my roles, so I invite them to represent my roles so they can raise objections from them if needed. You could also use it when someone senses a tension that limits your role, which you also sense but think for whatever reason that they'll do a better job resolving the tension than you would (e.g. perhaps they used to fill the role for a long time and you're new to it).