Not in any modern sense of the word, if the rumours are true then in all honesty the relation was so distant that we’d never consider her mixed race.

There is also no actual evidence at all that Madragana was African besides a few non-contemporary claims, many of which have been countered in greater measure by claims she was Iberian but born into and accepted elements of Arabic culture (a Mozarab, to use specific terminology) which was a fairly common. The claims that are made to imply Charlotte was ‘mixed race’ claim that she closely resembled African folk in her facial features (without ever attempting to isolate where exactly in Africa these features related to) but even were Madragana African it is extremely unlikely that the 24 generations removing the two would cause any physical similarity.