Hayes, who ended her 12-year reign in charge of the Blues at the end of last season, is back in London as her new side prepare for the match at Wembley.
The 48-year-old, who guided Chelsea to a fifth successive Women's Super League title in May, opened up about the toll the job took on her health, highlighting the perks of international football.
"I don't have to sacrifice the things that made me healthy," she said on Monday. "I didn't feel healthy at the end, I actually felt unwell at the end of my time at Chelsea.
"It wasn't pressure, it was the stress and toll it took on me and doing that during menopause was even harder.
"To get on top of all of those things, I've got my mojo back and my smile and enjoyment back, which I didn't realise I had lost."
Hayes guided the USA to Olympic gold in Paris in August and Saturday's friendly will be the first time she has come up against Sarina Wiegman's Lionesses.
She admitted it would be strange going up against players she has "gone to war with" but said the occasion was strictly business.
"I'm looking forward to seeing Sarina," she said. "Of course I need to go through a weird moment when the national anthems are being played. I'll hum along to it (God Save the King) being the English person I am, but also the same for the US one because I love it, I love both anthems.
"Beyond that weird moment and coming up against players I've gone to war with, it's business come kick-off. I hope it's an entertaining game and a sell-out."
