Yeah, even if you have 2 vanguards, the skill will still activate because Foo is counted as "an entity" or the "3rd vanguard" for her skill. This, however, only applies to her skill only. Other skills that require certain ship quantity to activate (Like Amagi skill) won't count Foo as "an entity".
Also, there's an interesting activation if you pair her with Shiranui. Foo will flee away and the skill will be deactivated. I thought this is because Shiranui's ghost scared Foo or Foo is scared of another ghost. But, this is not the case, I've paired Kasumi with other ships who have a ghost (Like Kagerou) and Kasumi skill still activates. So, Foo will only flee if Kasumi is paired with Shiranui.
And a side note, I love how the artist is really putting his effort to make us know who's talking.
This bubble top part's shape is Isuzu's horn and ribbon. I asked if it's really Isuzu's horn and ribbon-shaped and he replied yes because he already put Isuzu's head in another bubble in the same panel, he played with this bubble shape to look like her. I really love this.