My opinion is that you should send it back. I have several reasons for saying this. First, she may not require a dildo to masturbate. Women need to have their clitoris stimulated, and a hard dildo may not be the best implement for this. She may prefer her fingers or a jet of water, or perhaps a vibrator, though a vibrator may provide very strong sensations and if she gets hooked on those, it could cause a problem later on. And since you’re already jealous of this dildo, I don’t think it will be good for you, or your relationship, for you to be away from her imagining what she’s doing with this particular dildo. If she wants one, because the sensations of being penetrated will help her to achieve orgasm, that’s fine but then if she decides to get one, better that it be one of her own choosing, and that she can dispose of before you get back, so that you can’t picture what she is doing.  The thought that you didn’t want her to feel sexually frustrated while you were gone was a good one, but it doesn’t seem as if the method you chose to express that thought really works for the two of you, so my advice is not to give it to her, if it’s not too late.