But it's almost certain that Tina's gender has played a significant part in moulding her personality as it is today (just like lots of other things will have) - given other people's perception of her, and the social conventions which fall to women and so forth.
Broadly speaking, you would be able to group some characteristics/personality traits into 'Male and Female' and I think the show benefits from typically 'Female' attributes too. One of those attributes is when the girls on the show castigate Dave for making a mildly sexist comment, which I find very funny - and doesn't have the same impact coming from Aled. I miss Rachel
I agree that a woman wouldn't add to Top Gear, just pointing out that the style of humour is stereotypically male-centric, which can put a lot of people off - as it can feel like too much of the same.