Maybe he meant first match on the WTA in 21 months, not ITF.
Did Fran have surgery? Thats quite a long lay off
What the commentator said was return to main draw action after 21 months, which is correct when referring to her first main draw match at tour level and is a bit different to saying she's been out for 21 months. That is explained by a mixture of ranking and injury. Her ranking accounts for some of the 21 months as she wasn't and isn't (with the PR) ranked high enough to get regular entry into main draws at tour level. After July 2021 she mainly played ITF and only played at tour level USO qualifying in 2021 and qualifying in Adelaide and AO in 2022, where she retired. This is only her 2nd ever direct entry to a tour level main draw, with the 5 other tour main draws she has played being WCs and a couple where she qualified.
I watched most of the match and although it really is a fantastic result I didn't see anything from Parrizas Diaz that suggested she was a top 100 player. She did not look comfortable on clay, her footwork was terrible at times with her lunging at balls (especially on the backhand) as if she just was too far away from the ball. Fran also served 14 double faults, I feel like that was a bit of an achilles heel for her before her long layoff.
Well done Fran though for taking advantage, very good scheduling by her/her team.