Sister Friede is too easy with Gael

I made a couple of solo attempts before summoning Gael (I hadn't seen the summoning sign before). I never use summons, but since the sign was there even without being embered, I assumed it was like a default game mechanic (perhaps lore-related), so I did it, and it completely ruined the fight.

Phase 1 was pretty easy, Phase 2 was a joke (with Gael, of course), and Phase 3 was absolutely underwhelming as she was staggered like 80% of the time. It took two tries, zero satisfaction.

Is there a way to respawn her?