How is that hearsay if she's directly testifying to her own whereabouts?
Hearsay would be if someone else was testifying "she was in X location on july 10th between 3 and 4pm", without the accused being available for cross
"I was at the library" is firsthand testimony.
"I saw her at the library" is firsthand testimony.
"I saw her library card in her pocket" is firsthand testimony.
"She was at the library - Bob told me so" is hearsay. Just look at the word - "hear say". Hearsay is testifying about events where your knowledge does not come from your own firsthand observations of the event itself.