Under the right circumstances, Price of Power can work well with Saki's hyper as the player will be able to start using her hyper at Norma level 2 instead of the usual 3. It is by no means a "must have" but can be useful if its the player's starting card.
With Saki's low health stat and sole reliance on her evasion, most battle cards are the best counters to Saki as they will not improve her combat ability much and will help the player KO her if she rolls poorly.
Sealed Memories is an excellent counter card to Saki, as she relies on the element of surprise regarding the contents of her hand and thus her traps.
Gift Exchange and Scrambled Eve are brutal against Saki as they can help her lose her hyper before she has the chance to set it. The former may also give the player her hyper, which can play out poorly for the opponent. Brutal Prank and Present Thief can also be used, but carry the inherent danger of Saki being able to use them to trick the player since they are trap cards.