I don't remember ever saying something like "林小姐你是老師是無?" but only "林小姐,汝是老師,是mī?".
Sī--mī is the short form of 是毋是. And the answer will either be 是 (sī) or 毋是 (m-sī or often just mī with long m).
In my usage, 是無 is paired with 是有, e.g. 汝是有來過,是無? But usually I omit 是, so just 汝有來過,無?
Others "adopt" the ending pitch of the preceding element.
Ah, thank you for confirming this! In my variant, pronouns are kind of belong to this category. I used to puzzled over these:
予伊/汝/我 -> hō·--i/li·/gua (all i/li·/gua become T7)
招伊/汝/我 -> tsio--i/li·/gua (all i/li·/gua become T1)
But if preceding by other tones, the pronouns are in usual low neutral tone (軽聲).
With the low-tone khinsiann elements, there's always a temptation for speakers of dialects with low citation T3 to "interpret" them as being not khinsiann, but rather T3. Even Maryknoll does this with "--kuè" (過), interpreting it as just "kuè".
My variant also has low citation T3, and indeed 軽聲 is similar although still distinguishable as T3 is longer while 軽聲 is short and "chopped".