"She was leaning" is simple past progressive tense.
"She was leaned" is either simple past passive or 'leaned' is used adjectivally. In this case, it's adjectival, since it's unlikely that someone else leaned her there.
"The ladder was leaning/leaned against the wall". The latter can be either passive or adjectival. The passive meaning is that someone was leaning the ladder against the wall. The adjectival meaning is that the ladder was in the state of having been leaned against the wall.
There's nothing special about this verb though. Many others can work this way.
"The car was backing out of the garage; The car was backed out of the garage." (As above)
"The knife was lying on the table (progressive); The knife was lain on the table." This is passive - the knife can't lie itself).
"The cat was sitting/sat on the sofa". "Sat" as above, more likely passive.
Student or Learner