You may have a bad shift cable that’s binding when trying to go to the smallest chain ring. It could also be the derailleur is binding due to rust as it sounds like no one ever shifted to that small chain ring. I would disconnect the cable from the shifter and work the shifter manually and pull the cable back and forth in the casings to check for binding. It could also be the shifter. Grip and trigger shifters need to be cleaned and lubed from time to time. I picked up a Specialized Hybrid with the same drive train and most likely shifters as yours and I immediately noticed the shifters were binding up preventing proper operation. I removed the covers to clean and lube them and install new cables and found a wasp had build a mud nest inside them.