Technically, this is completely possible. However, I see two potential problems:
They may accidentally admit her on the K-1 visa instead of on VWP, because they see the visa and get confused, since it's atypical to not use the visa. If this happens, it will use up her single-use K-1 visa and mean that she probably won't be able to go on the vacation to Jamaica.
They may deny her entry on VWP due to immigrant intent, because it is so easy for her to change her mind at any time after entering and stay and marry and adjust status as her spouse is a US citizen.