The crossover status of any given Love Live meeting is confusing, particularly when it comes to Nijigasaki and Liella. The three main-line anime installments — SIP, Sunshine, and Superstar — seem to take place around five years apart (explicitly stated for SIP and Sunrise, and conjectured in Superstar from the fact that Ren's mom, ten years before the present, seemed to be contemporary with A-Rise), but the Nijigasaki anime is completely unmoored from anything that would indicate where in the timeline it is.
Meanwhile, SIFAS takes place in an alternate universe where at least μ's, Aqours, and Nijigasaki are all operating simultaneously, and I think everyone is co-active in SIF and probably will be so in the upcoming SIF 2.
Tl;dr: A meeting between Superstar and Nijigasaki characters feels like it's a crossover right now, but one between SIP and Sunshine ones doesn't; this feeling is subject to change when new material comes out.