My 85 pound male's neck measures about 20 inches. Most collars have adjustment room so I would look at something in the 20 inch range.
I think your tracking collar has a gps to tell you where she is.
PTE,AC,URO3,AG2,UCD Xtra!Xtra! v. TeMar CDX,GN,RE,CGC,TC,HIC, Bh "Havoc" 6/4/07
PAM, URO3, UCD, UACH Tidmores Rising Star Lydia "Mayhem" CD,BN,RE,AX,AJP,OFP,P1J,CA,DN,HT,TKN,TC,CGCA 4/4/12
Lucky, Wolf, Max, Kayos - gone not forgotten.