I'm glad someone brought this up. She might be referring to Sekai, but I think it's actually Chiaki. Here's the line:
I can't remember if it's been established that Chiaki had a temper, but I imagine Chika is emulating her when she curses in Tagalog.
In "Curry Night" Chiaki talks about having a friend take Chinami to the hospital.
The friend is strangely intimidating and has connections; sure sounds like Tsubasa to me.
I also think this makes a lot of sense with Tsubasa's actions. The meeting at the hot spring always felt engineered, and she was remarkably quick to latch onto the Chosokabes as her "new daughters". My guess is she's been keeping tabs on them since Chiaki died and finally decided to get directly involved in their lives.
As for how they could have met, Tsubasa used to "sneak away" from her rich girl lifestyle in her youth: