Thanks for your question.
I am glad that you have asked this question.The risk of contracting HIV this way would be practically zero.The HIV virus is not a hardy one and is killed on exposure to air.
Unless she used it inside her genitalia and immediately used it on the exposed mucosa of your genitalia you are not at risk of getting HIV from it.
Considering that the vibrator was applied only to intact skin of shaft of penis and scrotum the risk of transmission is nil.
Please don't loose any sleep over this.
Reply if you need any clarification.
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Even for other STI's if exposure was from vibrator to skin the risk would not be there as even other virus like HSV and HPV are also fragile and die when exposed to air.
Other bacteria like gonorrhea need sexual intercourse to get transmitted.