Other respondents are absolutely in that, if this is not a direction that you're comfortable with as a player, it sounds like you need to have a discussion with your GM and/or group.
There's also the issue of player knowledge vs. character knowledge. If your PC has no idea that the rogue might turn on him/her, then there's little that you can do to prepare without metagaming.
The rest of my answer will assume that you as a player are more or less comfortable with how the game is going, that your PC knows about the danger, and that you're asking what steps your PC would logically take to protect himself/herself against assassination.
I think the first thing that most people would do in this situation is find others that they can trust to help keep them safe. If your PC isn't sure that the other members of the party have his/her back, the next step would probably be other members of your church. Fortunately, your PC is a worshipper of Pharasma, who has temples all over the world that would likely help protect him/her.
In fact, if your PC has other cleric friends and the money to spend, maybe surviving the assassination attempt isn't as important as making sure that someone knows how to find your PC and bring him/her back from the dead if he/she is killed. The Sending spell lets you send such a message across long distances, although you need 10 minutes to cast it.
The problem with other preparations is that as an oracle, your PC's defenses are already largely chosen. This, unfortunately, makes you a very easy target for assassination if your opponents know your spell list. Since I don't know your spell list, I'm going to throw out some suggestions and leave it to you to adapt them to your spell list and available resources.
Some spells you might want to have on hand are:
The Symbol spells like Symbol of Sleep are expensive, but they can be given specific trigger conditions and attuned to prevent them from working against certain targets. Your DM sets the limits on exactly what is possible. For example, the spell description talks about it being "displayed in a prominent location" - some DMs might require this to be above a doorway, but I've heard of other players keeping them inscribed on plates in their pockets to be revealed at the right moment. Another advantage is that once the symbol is set up, it doesn't take a spell slot.
Your PC could try to brand the rogue with a Mark of Justice that triggers if she ever tries to attack your PC. You could try this while the rogue is asleep, or if your PC thinks the other party members will have his/her back, your PC could confront the rogue openly and demand that she submit to this or your PC will leave the group and find others to help save the world (not because you actually want your PC to leave, but because that's what your PC would reasonably do if they felt threatened by a party member).