If it helps, if I heard loud farty noises, it wouldn't even occur to me to think they weren't coming from a bum.
If I were you, I'd sidle up to your work colleague and make a joke of it. Just say something along the lines of "don't worry, you're safe to stand next to me today! I've been trying some new supplements/diet pills/a new diet and it's just not agreed with me so I've got rid and I feel loads better already" and leave it at that.
Don't worry too much, it's only a bit of wind after all (as far as she knows!) doubt she'd tell anyone. Would you tell everyone at work if you heard her farting in the loo?