How to convince my wife that working out won't make her arms huge?

My wife is fairly slim and petite but says she wants to lose some weight and tone up a bit.

I’ve told her I would show her how to lift weights because one of the places she’s concerned about is the back of her upper arms, which are a bit flabby.

But she’s afraid she’s going to become big and muscley like me.

She has pointed out some famous women who work out and I agree that their arms do look big.

What should I tell her?