Meaning and paraphrasing

Theresa May made a transition deal her top Brexit priority at this week’s EU summit.(could you please define the meaning of this sentence and tell me why there is a "her" in this sentence?) But even as EU leaders call for the British prime minister to make more concessions(Does this mean RIGHT here?) to start transition talks, problems are emerging with the very idea of keeping the status quo for two more years after Brexit in 2019. “Transition is not what it seems,” says a senior Eurozone official, who jokes that the concept almost amounts to “fool’s gold”. A transition deal is a great prize for British negotiators because it provides business with two precious commodities: extra time and more regulatory certainty. Companies need legally binding assurances about the next 12 months. The problem is that guarantees may be insufficiently binding to meet such needs. A UK-EU transition agreement could also cover less than proponents might hope while a two-year deal may only delay the challenges Britain confronts. Brexit is a political negotiation, set to the two-year timeline of the Article 50 exit clause. That means any transition deal will ultimately depend on a final UK-EU exit agreement and ratification by the European Parliament. In the old Brussels mantra, nothing is agreed until everything is agreed — a moment that may come only in 2019.