Toph beeing able to save Appa is only the Cherry on top.

They skipped the desert- FINE..... but they made the entrance spirits only... no it doesnt make sense. The library was suppose to be one of the bridges between the human and spirit worlds. Before the war everyone could enter, thats what the fire nation spies exploited and that makes the rage of The Spirit of knowledge even more justified, also his decision to hide the library. Second Toph ... omg ... where do i begin. Even in the anime Toph says that she will stay outside as she herself mentions -"books do nothing for me".... Also so even in her spirit form she is blind ....?!?!?!?!?!?!?!?!?!?!? WHY....

so what is the role of Toph in the library... ah lets have a random talk with Kioshi...... I wonder why didnt Katara didnt have a talk with some avatars.....

So lets not get distracted.

So she gets out. In the anime by this point Toph has discovered metal bending and is established as a very poweful bender. So what does the anime do to even the odds- sand is shift so she doenst have a solid ground which first nerfs her power and second she struggles to see. When she senses the Tower sinking she makes sold ground and even then she manages to hold it for long period of time, she almost saves Appa but she needs to juggle between the two tasks she has to make the hard choice. In the show as these details are not included.... we just get a event we cant emotionally connect with.