Some years ago, I got similar comments from big, boofy blokes; because I rode a Kawasaki Z1000R - not exactly a "small" bike for the times. My standard reply to "How on earth does a little girl like you manage a big bike like that?" was "Sweetie, it's not the size that counts, it's the skill." For the record, I didn't consider myself "small" at 5'6", though I was slender. It's true they were quite a bit bigger than me, though. It's as much about attitude and ability as anything, in my book.
Don't give her the upper hand. Simply give back comments that emphasise your ability, your prowess, your sporting skill, your strength (as opposed to sheer mass, which she seems to think "wins"). Anyone observing will form their own opinions of her insecurities, and applaud your ability to remain calm under provocation. Wit beats cattiness anyday!