Let's Roll!
She would destroy Hillary.
Actually, she wouldn't. You need an elective-office resume', which Hillary now has and Peggy hasn't. She needs to start somewhere -- city, county, state legislative office. Then work up to governor, if she's going to take on the likes of Hillary. Hillary's got too big a head start, since she began as a senator (sorta like being hired as an executive VP for your first job).
The road up to the presidency is either senator-VP-president or governor-president. No senator has been successful campaigning for the presidency since Jack Kennedy got the Chicago graveyard vote from Mob gargoyle Sam "Momo" Giancana.
Before Jack, you'd have to go back to.....perhaps Calvin Coolidge, or Warren Harding. I'm not sure what Wilson was. But you would have to go back a very long way to find a sitting senator who was elected president.