Tell your girlfriend she is really good! And should keep doing pixelart.
I’m amazed at what you made even though you are just starting with LÖVE.
I think the best way to learn your way around LÖVE is to try all the different APIs and things it has to offer. And also knowing Lua entirely (LuaJIT more specifically), even things like performance and optimizations. Just be sure to work up slowly cause there is a lot to learn.
The rest you’ll figure out just from working with it. But if you really need to, there are tutorials here and you can always come to the Discord server or the forums to ask questions
If you can, you should also try to learn common Game Programming Patterns, you may already know some of these though.