The first solution I came up with does technically require a choice, but it isn't meaningful, so it didn't bother me.
The 2 cards are swindler, tactician.
Tactician will eat all of those lovely platinums, and the swindler hits an opponents tactician - which is the only other $5 card, which is empty, as are council rooms (for whatever reason). This forces the opponent to gain the final duchy, and the best that Sarah can buy is an estate.
Bonus points if the swindler destroyed a duchy (with tactician and council room piles empty), but Sarah still lost because she bought the estate to tie, but lost on turns because she is P1
A twist on Gendo's solution:
- double swindler hits double peddler with 2 provinces and 0 peddlers remaining, giving her opponent a 17 point lead and ending the game - and even buying a $34 colony doesn't fix it.
My favorite solution is the embargo one.