Uhh.. So how did Valeria create a portal to the Soul Cairn? reading some lore, it seems that its extremely difficult to make a portal from Mundus to Oblivion. and that it requires a sigil stone which is messy business unless you convince a dremora to go fetch it for you directly. and even then you'll need a daedric lord to help you. and when all of that is done, the portal is pretty weak and can only stay open for a few mins. which makes all of this pretty useless. even Fyr had to exploit a series of portals to various realms to make it work according to The Doors of Oblivion. so how did a vampire create a portal using some random Ingredients she found in her old dusty laboratory? was that circle already built to connect to the soul cairn and she needed a few ingredients to open it up? because that seems like the only logical answer.

Well remember that she's a centuries-old sorceress, and that there are always loopholes. Remember that she didn't make a complete porrtal either.

She made a link, with the willing aid of the Ideal Masters, to a realm of Oblivion that isn't quote the same as all the others, and to boot no living thing can pass through it, which took her a very long time to make.

Also, those ingredients are extremely specialized versions of things that people who aren't superpowered adventurers would have a good deal of trouble getting, and that they were only there to activate the portal rather than create it.

In short form, it's harder than gameplay made it look, but it isn't impossible, especially considering how little we know of the nature of the Ideal Masters.