If I Smokescreen and kill an Irelia with Guardians Angel attached at a battlefield, does she still have -4 when she recalls to base?

Yes, Irelia will still have the -4 Might effect applied to her when she is recalled to your base.

According to Rule 453.1: "Unless otherwise stated by the source of the Recall, Damage, Exhausted Status, Buffed Status, and applied Layer alterations will all remain unaffected by a Recall."

Sequence of Events:

1. Smoke Screen is played, targeting Irelia. It applies a -4 Might effect to her that lasts until the end of the turn.
2. A "kill" effect is applied to Irelia (e.g., from an attack or another spell).
3. Guardian Angel triggers as a replacement effect: it is destroyed, and Irelia is healed, exhausted, and recalled to your base.
4. Because the -4 Might effect from Smoke Screen is a "layer alteration" (a continuous effect applied until the end of the turn), it persists on Irelia even after she is recalled to your base.

Nuance:

• Healing vs. Buffs/Debuffs: Healing only removes damage marked on a unit; it does not remove continuous effects like the -4 Might from Smoke Screen.
• Persistence: Since the effect is defined as lasting "this turn," it will continue to apply to Irelia at your base until the turn ends.