Need a reasonable explanation for her to buy heels

[Brevelyn]

A woman I am very close with, is a shoe addict. She has unknowingly provided several pair for my pleasure. She would probably choose and even buy a pair for me, if I could provide a reasonable explanation. (She has already told me that men wearing heels is a complete turn-off) She still accepts and models shoes/boots I buy her, and occasionally sends pics for masturbation.
There's just something about wearing something she likes, while I cream into one of her "aquired" pair. I need a plausible reason for her to shop.
- I considered telling her it was some sort of ridiculous bet. Win / lose, whatever.
- A cause or "walk" seemed plausible, but she might want to participate.

And ideas or suggestions?

[mi13ke]

You are both invited to a fancy dress function, and you will go as a women, which gets cancelled at the last minute.