(Girls only) Girls how do i let a girl know its ok to?

The way i feel is that i have absolutely no problems with girls farting, its a natural bodily function and i wouldn't want my girl holding it in and feeling all uncomfortable, bloated and getting a sore tummy. If a girl was siting on my knee even i would think don't worry about moving just let it out. So how would i let a girl know its ok and convince her to just let it rip when she needs to.