Congratulations on getting your Norah a cage mate! Rats really do need to be at least in pairs
They are such social animals.
If they are both very young still, it shouldn't be much of a problem to introduce them to each other.
Introduce them to each other on neutral territory, somewhere Norah has never been before. The bathtub works fine for this. Give them some time to sniff each other, to get to know each other. If everything seems to go well, put them both in a completely cleaned and empty cage. Make sure it's newly cleaned, so it doesn't smell off Norah; otherwise she might see this as her territory, and the other rat as an intruder.
Don't give them any toys they can hide in just yet, no tubes, no boxes, no houses. Else they can hide from each other, and everything will take longer.
Might be that they will fight a little, but this is almost always just to determine who is the boss. Don't interfere, let them figure this out for themselves. if you keep breaking them up at this stage, it will only prolong the process, and add to their stress level. A good rule is; no blood, no harm.
If everything goes well in a few days, add a few of their stuff back. If it continues to go well, re-add some more after a few days. And so on. If it gets worse, take stuff out again.
If they're still young, this shouldn't take long at all. Young rats fall outside of the ranking system until about 4 to 6 months of age, so two rittens won't fight a whole lot.
Might be as they get older, they'll suddenly start fighting for a few weeks. Again, nothing to be scared about, they'll just need to decide who is going to be alpha.
Good luck!