。
She's one of my friends.
Literal
She [topic-は] my friends [of-の] one-person is.
The partitive frame ~の１人 ('one of') singles out one element from a named set — same pattern as ~の中の一人 with the 中の elided for brevity. Both forms are common; the leaner ~の１人 is more conversational. The Arabic １ in mixed-script style is typical for casual or modern writing — a kanji 一 would do the same job in more formal text. 友だち (friend) here is partly written in hiragana, a common stylistic choice that softens the appearance versus the all-kanji 友達.