The reigning world and Nations League champions had their plans disrupted a few days before the tournament as Bonmati was hospitalised with suspected viral meningitis, but the 27-year-old said she is back to her best ahead of the Swiss showdown.
"I never thought I wouldn't be here - I thought I may miss some games, but I never thought I couldn't be here. I'm willing to be in this tournament. What happened was an unexpected thing," she told reporters on Thursday.
"I felt super well physically, I was perfect ... and all of a sudden, I was at the hospital. It was a new experience for me, obviously, I was negative because it was five days before starting the tournament and I was at the hospital.
"I was frustrated, I suffered, I must admit. All players want to enjoy tournaments but luckily enough I'm ready to play the quarter-finals."
A win against the Swiss would set Spain up for a meeting with either France or Germany in the semi-finals, but Bonmati said she wasn't looking that far ahead.
"For tomorrow, it's a new challenge for us, we have the possibility to be in the semi-finals. My objective is to try to continue writing history," the two-time Ballon d'Or winner said.