They spend an entire year post-Arc 4 practicing, learning, and creating new spells/strategies.
In Arc 5, Subaru and Beatrice are together until an exceptional circumstance- Beatrice going into hibernation after trying heal wounds caused by Wrath & Greed- seperates them temporarily.
In Arc 6, Subaru and Beatrice are together the whole time.
In Arc 7, Subaru and Beatrice are seperated by an exceptional circumstance- Subaru being teleported to the other side of the planet- and as soon as they reunite, they are together. Beatrice even spent 95% of the trip in hibernation to save her Betty batteries.
It is standard for a Spiritual Arts User to be able to use Spiritual Arts, that is something I feel is rather obvious. In typical circumstances Subaru has access to Beatrice, they are physically, spiritually, and emotionally bound together for their (Subaru's) whole life.
Plot seperating them to put pressure on Subaru is not a reason to make Betty non-standard, latter Arc 5 & Arc 7 are exceptions to the typical base state of Subaru and Betty being together, which is why seperating them creates tension at all.