I don't know if you use any mods that might cause this or if it is because she is a ghost or just that the power system remains a bit unstable following the C&D patch in November. I also don't know if you used any cheats to get to this point, but it does seem like there are still some strange things happening with vampires in general :/
I don't have this exactly, but it interests me that you have a weakness greyed out but selected. I have this in my game too:
https://i.imgur.com/WcgkZAo.png
As you can see if you look carefully, the restless sleep whatever it is weakness is greyed out but still has 1/2 selected. This has been the case for this sim since before the most recent patch. As you can also see, this sim has sun immunity even though he isn't at the right level to have it. He has never been an NPC so the game should not have allocated him this power. I have three other sims who have also obtained sun immunity at random without being the right level for it, and I still have times when powers grey out and can't be selected when things are chosen.
https://i.imgur.com/lORRDLb.png
Here is the above sim's son, also with sun immunity.
Although this relates to powers rather than weaknesses in his case, there is an anomaly here too which I think is related. For comparison, here is my grand master sim whose powers have been added normally and without any oddities:
https://i.imgur.com/yRRnp8U.png
In his case, the sun immunity is selected but shows 3/3. It is the same in the case of HIS son, who is the only other sim I have given full immunity to and who I have levelled all the way up to the top in this game:
https://i.imgur.com/gJN6jTJ.png
In the case of the other two, it's just there as selected but doesn't seem to have come about from allocating any points. It's just there.
Like the greyed out weakness that you and I both have, it's something the game seems to have control over, rather than the player. I feel like even if I did want to reset those sims like you are trying to do, probably I wouldn't get any points for sun immunity because it doesn't seem to have used any to select it.
If you didn't use mods or major cheats to get to this point, and I have no reason from what you said to assume that you did, it sounds to me like the vampire power bug from the november patch is still not totally fixed. The fact this happened in a new game makes me think so even more. Since the most recent patch (which should have fixed it) I have had at least one vampire with greyed out powers that I couldn't select, and it took a couple of tries to get them to be available. This points thing and greyed out selected weakness seems like it might be related.
Unfortunately I have no idea how to resolve it :/
