Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
Many women do enjoy using toys when with their partners, just because of they feeling more fulfilled that way, by more stimulation, and not because of fantasies around having a third person in their sexual relationship.
How to know? The only way to know is by asking her about it, by having and open, honest and direct communication. Emotional and sexual fulfillment depend on good emotional and sexual intimacy, and these are built by good dialogue between partners. Then share with her about it, for you to learn how she feels, what she wants and expects from you, so you could respect, support and fulfill her. This must be reciprocal for the relationship to work. Does it make sense?