That’s an interesting question, and one that can have a variety of answers, depending on your particular flavor of Paganism. In some Pagan traditions, people dedicate to a single god or goddess of that tradition’s pantheon. In other cases, they may dedicate to a pair of deities. Occasionally, people may feel a connection with deities from different pantheons altogether. It happens.
Human spirituality tends to be somewhat fluid, in that while we can honor one deity we can also be called by another. Does this mean the first no longer has any influence? Not at all – it simply means some other aspect of the Divine finds us interesting.
If you genuinely feel called by this second deity – and from your email, it seems pretty clear that you do – then I would consider exploring things more. Ask the first goddess if she would really be that offended if you honored another one in tandem with her. After all, the deities are distinctly different beings, so honoring a second goddess doesn’t necessarily mean any toes are getting stepped on.
If you're fortunate enough to have been tapped by the Divine, not just once, but twice, I'd regard it as a gift. My opinion would be that as long as neither deity has any objection to the presence or worship of the other, everything should be fine. Treat both with respect, and show them each the honor they deserve.