You survey your options.
Your girlfriend is much too large for you to take on with your bare hands.
In addition, aren't ants known for their incredible strength?
And now you're taking that strength and mulitpying it by about a thousand times it's original size.
No way you can win on your own.
It would have been nice to have an umbrella with you as a weapon. Oh well.
For now, your options are limited.