The Fashion designer - whose ex-husband Jude Law is believed to be engaged to the blonde beauty - admits hostility between her and the actress has finally calmed down, and things are " good" between them.
She said: "Things are good with Sienna."
Earlier this year, Sadie launched a twitter attack on Sienna, after the 'Factory Girl' star took Sadie and Jude's daughter Iris, nine, to have her hair cropped without checking with her mother first.
Although the pair are now on good terms, Sadie doesn't have any regrets about writing about how furious she was with Sienna at the time.
She added to the Daily Star newspaper: "I don't regret putting anything on twitter, though, but everything's fine now."
Sadie and Jude - who also have sons Rafferty, 14, and Rudy, eight, together - divorced in 2003 following six years of marriage.
Despite the emotional pain of the split, Sadie - who also has 20-year-old son Finlay with first husband Gary Kemp - recently admitted she still gets on well with Jude, who she split from in 2003.
She said: "We still have a very good relationship considering everything we've been through. I'm glad that he is happy and I know he only wishes me well.
"Me and Sienna have to have a relationship because I am a mother and she's got some kind of relationship with my children, but we have pretty much made it work. I like Sienna a lot, she's a great girl."
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