What a shame she doesn't understand its sentimental value. But unless you made it clear to her how important is means you handing it down to her, it's just a loose piece of cloth. Ex: My mom gave me a shadow box with her silk gloves she wore at her wedding (plus) a picture with her wearing them. Including the photo really made the difference. (: I'm just throwing out an idea-- incase you feel she still deserves keeping the handkerchief.

The dust might have been in your family for 4 generations also. If that's the case I don't blame her

Maybe explain to her it's importance and if she seems not to put more value on family heirlooms, then ask for it back and give it to someone who will treasure it as you do

I'm just imagining the ancient boogers she's spreading on her furniture. Anyone else?

Did you tell her it had been in the family for 4 generations? If not than perhaps you should have.

Spank her

you must have better heirlooms then a handkerchief. I mean thats a pretty lame one if you ask me. I would use it to dust too because it has no value other then dusting.

Explain the significance to her.

Cum towel? Wtf.

If it's just a plain handkerchief (ie no embroidery to set it apart, etc) is it possible she doesn't realize that she was using that particular handkerchief? I mean, I'm all for things with sentimental value... but a handkerchief? Besides, to be honest, if you've given it to her, it's now hers to do with as she wishes. You may regret having given it, but it's no longer yours.