I tried installing the xreplayser mod for Heroes, and it has it for female models, but it's static; no animations work.
What if I put Isabel on a horse from a male combat model?
In NHF, they did this – they used an effect to put female characters on a male horse so that the flag and standard-bearer would be part of the main model and could change the player's color.
If you just need Isabel with a standard-bearer, and changing the flag's color isn't necessary, you can make the flag and the man an effect.