Pulse is a palpable pressure wave in the arterial system indicative of effective operation of the cardiac pump. It is a good proxy for adequate circulation of the blood. Patients whose circulation fails tend to develop anoxic brain damage in a few minutes. The various cardiac electromechanical disorders mentioned by lompaseo may or may not be associated with circulatory collapse. Although 'flatline' aka asystole always and ventricular fibrillation almost always results in death if nobody intervenes.
I don't know for sure, but I have officiated at enough cardiac arrests to suspect that those involved were pretty desperate to have continued cpr for thirty minutes. What we don't know is how long she was in circulatory arrest before cpr was started. The fact that it went on for so long suggests to me that her condition is parlous. Especially since she's been admitted to ICU. I wish her well, but I fear the worst.