You wrote- On (54b) [55b] the example is given that one should not announce a person's illness on the first day as it is detrimental to his particular mazel. But, we say that there is no mazel for Israel and that we are above mazel?
We find the concept of detriment to (or from) a person's Mazal elsewhere (see Chagigah 5a, Horayos 12a). When the Gemara says "Ein Mazal l'Yisrael" (Shabbos 156a), it is referring to a Tzadik who is able to override the effects of his Mazal. Ordinary people, though, are subject to their Mazal.
Alternatively, "Ein Mazal l'Yisrael" refers to the nation as a whole. The Jewish nation is not subject to the effects of Mazal as are other nations. (See Insights to Kidushin 39:1 and Moed Katan 28:3; see also the explanation of Maharsha to the Gemara here in Berachos).
Y. Shaw
D.A.F.