The backdrop of why she came out to sing that song after 20 years of silence seems to have been to let everyone know that she had put her stamp of approval on Combs using her song to license, and sing his own version of it, which was a top country hit last year. Chapman herself reportedly earned north of $500,000 in royalties for it based on that licensing, thank you very much, and her own 1988 song enjoyed a startling revival in the charts. 

It was not without controversy, and Chapman did her best to shut it down: Wokesters had screamed that Combs was appropriating her music and claimed that her song never would have become a number one country hit without a white guy singing it. I wrote about that here and here.

Chapman put out this statement last July at the height of the controversy, a rare email from her as she is very shy, which should have killed off the matter immediately, but apparently didn't:

I never expected to find myself on the country charts, but I'm honored to be there. I'm happy for Luke and his success and grateful that new fans have found and embraced 'Fast Car.'

So, she did the performance with Combs to make sure they got the message.