I think the mistake is assuming this was just like energy movement, larxene was hijacking the remnants and Elsa's ice magic and mixing it with her own magic so she could control it. The whole place is a fusion of Larxene and Elsa's powers, you can see that in the design. Electrified ice traps and other sadistic machines design to kill you, a castle that pay homage to Castle Oblivion right down to having cheeky chain motifs in it, Larxene's symbol are ALLL over the place like on the walls but the overall giant structure is Elsa's signature snowflake.
Elsa's ice isn't just ice, it's magic in it of itself, it can co-exist without her once made such as Olaf and Marshmallow do, and other magic can interfere with it which is also a major premise of the second Frozen movie. So by leaving behind magical ice energy Larxene was able to hijack it by fusing her own lightning magic into it and thus she could grow and reshape the ice into what she wanted. Trace's of elsa's magic in the form of her signature snowflake is seen, but the whole thing itself is Larxene's designs twisting the magic of Elsa with her own influence.
This ties into another plot point, it's not just random, Larxene let Sora know Elsa's magic is volatile and will become what she believes it to be, it could turn into darkness or light, and that's why she refused to let him interfere. The ice maze is a representation of that, someone from the dark taking and twisting Elsa's volatile ice magic for her own ends, it shows how dangerous it can be depending on what messes with it.
*edit*
In fact I think a nuance that is often underappreciated is how elsa's magic has a distinct architectural look to it, the ice maze looks nothing like what Elsa would make. When Elsa is happy, confident, etc... her magic has a soft, fun, smooth, and rounded aesthetic with a detailed artistic look reflecting her creativity. When elsa is sad, upset, angry, etc.... her magic turns harsh, sharp in a deadly way not an artistic way, rough, and loses its creativity for a chunky bluntness to it. Marshmallow and Olaf are two perfect signs of this. Both are snowman but one is a lot less put together looking because one is made during her high point of let it go and the other is made out agitation and fear.
The ice maze isn't something Elsa could create. It's full of creativity but it's all creativity designed to harm, it's smooth but not rounded, it's harsh but not rough. It's deliberately malicious and purposeful in design, it was created with a clear intent to hurt and keep you lost, to toy with you and trap you. It's not meant to push you away it's meant to swallow you and make you suffer. Elsa is loneliness and distance it's Larxene who is enjoys in your face deeply personal suffering
It's not Elsa, it's Larxene all over.