The more conservative sectors of 1950s Argentine society would never tolerate a bastard born in poverty who married into wealth and power as a president. So, even if we assume the 1955 coup against Peron doesn't happen, Eva isn't running for president in the next elections.
What I could see, however, is an older Eva Peron running as Juan Peron's VP in 1973, just like OTL Peron's third wife did, and she would replace him as president when Juan Peron dies in 1974. An Eva Peron who lives decades longer than in OTL would naturally be far different at an ATL age of 55 than how she was at the age of 33. But I don't think she'd become more knowledgeable of economics nor more open to political compromises. That means her presidency would be very similar to Isabel Peron's tenure, although backed up by a prestige and myth Isabel Peron didn't have. Congress would not send her away and wouldn't dare to consider impeaching her. This ATL Eva Peron would, due the butterfly effect, surround herself with different people than Isabel Peron. But I think her tenure would be marked by economic mismanagement and State sponsored right wing terrorism just like Isabel Peron tenure was, and the military would either coup her, like they did to Isabel, or if her prestige remains strong despite the spiraling down economy, they'd carry out their plan to fight the political left wing with her as a president.
EDIT: And come to think of it, a democratically elected widowed Eva Peron serving as Videla's public face can make for a chilling TL