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it would depend what you do or say if you know what her motivation was. It also depends on your boyfriend's reaction. If you think that she really did not think much about this and there is no premeditated goal behind it, then you may decide that she just did not give it a whole lot of thought about what she's doing. If your boyfriend thinks that it is strange and agrees with you, then there is nothing for you to worry as far as his reaction.
If you believe that confronting her will bring some closure to how you feel, then you can try to ask her something in the line of what was with the card you sent and let her elaborate.
Even though you may not do something like this, others live by their own measures.
You may decide to wait for a short period of time just to see if anything else in her behavior hints at a possible reason.