The easiest model to identify should be #1, the 1998 Sears SR as she is supposed to have darker chestnut splatters over her back. If you had a variation without these spots, it might possible to mix her up with #2 (1990 Sears SR) and #4 (1991-1994 RR). #2 has more of a grey-tone to her chestnut colour than any of the others in the group and only comes in old plastic.
#4 came in two main variations - sandy bay and chestnut. The chestnut variation is more of a red brown than the other chestnut models and has red-ish points close to her body colour, and grey hooves on the legs with socks - #1 has tan hooves on those legs.
The bay version of #4, the #5019 Standing Thoroughbred (1991-1994), can be a bit difficult to tell apart from the other bays. Her mane and tail can be charcoal to nearly black, but often ranges from chocolate to a brown close to her body colour. Unlike #3, #4, and #5, her hocks lack shading which makes the darker forelegs, especial on the charcoal legged models, look decidedly odd. She comes in new and old plastic which could, depending on plastic type, be used to differentiate her from the only-old-plastic Citation and the only-new-plastic Saddle Club mare (#3).
#5 and #6 are variations of the bay #5020 Citation (1975-1990) and were only ever available in old plastic. The original Citation release should have an off-hind sock, but a variety of leg markings are possible. The similar looking buckskin/sandy bay mare from the #5650 Saddle Club Collection II (1996-97) was only made in new plastic and tends to be much more tan than many of the original Citations and usually has four white to cream hooves, if not socks.