I will assume this is a pure H2H fight.
I will also give the win to Captain America.
Let me explain: Cassandra is by far the more skilled (in ways that Steve Rogers could not even comprehend .....she is so skilled that for a while her speech faculties in her brain were vestigial due to the total take-over of the physical component ....she 'talked' violence).
She is also perfect in terms of timing, combat cadence, and the ability to read an opponent that Steve Rogers would also NOT be able to comprehend. Her way of fighting is beyond anything that Steve could comprehend .....beyond even Batman's methodology. Steve and Bruce are perfect, but Cassandra is something else. It is like the difference between someone who is EXTREMELY good at math (and gets 100% in all mathematical exams), and someone who is a GENIUS at math, and can calculate 10 digit figure equations with his mind in the sequence of a second and has no idea how they do it.
When Batgirl had lost her combat reading powers, she asked Batman how long it would take for her to learn defence to be good enough for the costume. He said 1 year. She then asked how long it would take for her to be as good as him. He said 10 years. However, she would never be as good as she was before she lost her abilities (later Lady Shiva gave her back those abilities, and when she had them back Batman couldn't even land ONE blow on her. He might as well have been standing still).
However, Captain America wins this fight.
How, after I've explained that Cassie is basically ...well ....beyond physicality?
Simply by looking at the trouble she was having with Deathstroke, and the trouble Iron Fist was having with Captain America.
When Cassie was fighting against Slade, she was having serious difficulty. The thing is Slade is a certain type of meta, who has perfect flow. He is not as good as her, but he is very fast, and motion for him is ....well ....perfect. In her own words, she couldn't read him because every movement he made was like a VERY LOUD choir singing VERY FAST.
Now look at Iron Fist and Captain America. Similar situation when they faced off .....in fact in the scan you can see Danny saying that Steve's martial arts skill is BASIC, but that he is so fast and perfect in motion that hitting the darn guy is just hard nuts!
Similar situations.
What is fact is that reading Steve would be hard for Cassie ....not as hard as reading Slade, but still hard (maybe at the same level as trying to read Ravager ....who was also a 'choir,' but not as loud and not as fast, meaning that Cassie was able to engage her with some effort and win). Steve would be between Ravager and Slade, meaning that even though Cassie might still read him, it would not be the advantage it would be with another fighter.
The advantage here is Captain America's, and he should win a good number. It will not be 10/10 ....actually more like 6/10.
But a win is a win.
Caveat: However, if I want to be a b!tch I can include a caveat. Looking at the Steve vs Bruce fights, they were basically equal ...but it was stated that if it went on for long enough Captain America would win. However, for them to be equal in the short-term, means that it is possible for Batgirl (using her skills and abilities) to pull in a number of wins.
Anyways, for now Captain America