Your sentence is a bit too complicated and it kind of feels grammatically awkward, but it would be understood in context.
Yet, a shorter sentence might work better. Some proposals:
-Esa blusa es/está tan escotada, que mejor no se la hubiera puesto. ("Estar" works here, because the speaker might be thinking there may be some arrangement to fix the problem.)
- ...que (mejor) no debería habérsela puesto.
- ...que no debió/debía ponérsela.
- ...que ni (siquiera) se la hubiera puesto. (Without "siquiera" is a bit) colloquial.)
As for your sentence:
Esa blusa
es tan escotada que
ella más bien podría ni siquiera haberla
llevado puesta.
Or:
Esa blusa
es tan escotada que más bien podría no haberla
llevado puesta.
Notes:
1) I think "más bien" and "ni siquiera" don't work well together, so it's one or the other.
2) "Haber llevado" is a whole conjugation, so the past participle doesn't agree with the subject.
3) Even with these changes, the sentence is too complicated for daily speech, but it would be definitely understood in context and it would be grammatically correct.
