Since her first short trip to the city, Lisa has been planning her next trip with a high level of <u>interest</u>.
"Since her first short trip the to city", describes she has been on a trip before and is planning to do another. So this shows her determination to go on another.
It would also make sense to place 'interest' in the sentence because, if you have been somewhere and are eager to plan another trip to somewhere again you would want to have at least somewhat interest and fascination.
