This one is a little sticky. Several characters reference gods that only exist in name and concept in that character's story and play. So you could come up with something totally new, use it in play, and do so without having to do a full deity proposal, especially since a paladin doesn't exactly derive any different mechanical benefits from one deity over another. I'd say go for it, especially if the stereotypical Protector/Sun god type (Helerion, no write-up but is the go to paladin deity in the Baronies that featured in a couple of adventures.) doesn't appeal to you.
On the other hand, if you want to do a full deity proposal feel free to do so.