The 36-year-old told British Closer magazine that Geordie Cole, 28, only ended her relationship with the Chelsea star because she felt like she had to after his infidelity.
She said: 'The next chance will be Ashley's last chance, there's no doubt about that. Cheryl's a lot stronger than she was two years ago. The relationship will be on her terms. It will be her who wears the trousers this time, and he won't be able to put a foot wrong.'
The star added: 'He really hurt her and I couldn't at the time ever see her taking him back.
'She really loved him and didn't want to get divorced, she just felt she had no choice. But she needs to follow her own heart.'
The Big Girls Don't Cry hitmaker, who is married to actor Josh Duhamel, thinks the Promise This singer should just do what she wants.
She said: 'It's easy for people to say she's crazy for taking him back but life isn't as simple as that.
'If love is still there and she truly believes he's changed then she should go for it if that's what she wants.
'It doesn't matter what her family, friends, or her management team say, it's her life and her decision.'
Fergie added: 'She's a very traditional girl at heart and wants kids and to grow old with somebody.
'She is really strong now, and if she does decide to give him another chance he's going to have to be the perfect husband because it's her dream to be the perfect wife and mother.'
Ashley, 30, was accused of several affairs throughout their four-year marriage, which led to her divorcing him in September last year.