Tsikhanouskaya has no government and cannot be recognized as a legitimate president, only as opposition leader. There are only indications that she may have got popular vote, but until there are free and transparent elections it is only a rumor - not enough for recognition by democratic standards.
In this role the only topic that can be discussed with her is the peaceful transition of power and organization of new elections - until they happen, there is no recognized government and no negotiation party.
Active non-recognition can be a good option here: since there is no recognized government, in all applicable cases (events, elections in international organizations etc) it shall be decided that Belarus abstained from vote or was absent. Membership and contractual payments from Belarus can be rejected and considered not happening, resulting in suspensions, sanctions and cancellations and so on and so on.