Yes as others have said its one of two cards which came with the bed and crib set. The bed and crib set is hard to find - but as a set it seems to turn up MIB and complete more often than it does loose and in parts...weirdly.
I would not sell it in an auction with her. In comparison to the pony herself and the twins, the card does not add enough of a value to hike the end auction price. I would sell it separately. I think Sunshines price of $5-6 is fair for what it is.