Thanks
@Muleski for the shoutout, but I'm not sure I have much to add to the discussion as I have no empirical data and have not taken part in ski testing either last year or this season, to mention nothing of the fact I don't know anything about skier cross. I tend to size skis for junior athletes by height and technical efficiency more than by weight. Flex of the ski is a bit of an X-factor that needs to be considered. For example, I put a very strong and technically efficient U10 boy on 122 SL and IIRC 144 GS Rossignols because they were very stiff, much moreso than other sizes. I know it's cliché but this is really a conversation to have with her coaches for two reasons. First, they know her skiing and can provide the best recommendation. Second, they may have information on club demo days or know of reps who can provide demo skis.
All that aside, all skis are not equal. This isn't to say that one is necessarily better than another, but they are different. Also, while most skier cross athletes use a GS ski, SX is not GS and you will want different qualities in the ski. Many of my athletes like the feel of a livlier GS ski, but in SX I would think a smoother feeling ski that takes less input from the snow surface would be beneficial. Heads and Fischers tend to be damper, smoother skis while Rossi/Dynastar and Nordica tend to be a bit snappier. Rossignol has skis available in several lenghts, sidecuts and flexes, but they aren't obvious. In the example above, I put that boy in the 122 slalom because the 132 slalom was very soft and the 122 felt like a pint size world cup ski.
Off the top of my head, I would say to look for about a 135-140 GS, 14m radius that can change directions quickly (doesn't really get locked into a turn), but is stiff enough not to take snow input and won't throw her if the ski is unloaded quickly. Honestly, I wouldn't sweat it. It is very hard to get a bad ski. The Nordica GS in a 135 or 142 is great and will be a little quicker feeling than some other skis without feeling snappy. The Head that you are looking at, probably in a 138 would be a great option. Either the Dynastar or Rossignol GS with the R20 plate in the 135 is an option but also look at the 144 in that ski, even if it seems a touch long. A lot of kids really like Fischers, Volkls, and Atomics but I don't know much about them, though Fischers are very popular because they are heavy and damp, but still soft and supple. I had a U14 girl who went back and forth between Fischers and Dynastars this year, arguably skis at opposite ends of the spectrum (Dynastars tend to be light and stiff). She has always skied Dynastars and ultimately ended up on them, but I noticed that on race days she would always warm up on the Fischer because the soft, damp, supple feel became her security blanket. After a few runs on them, the world was good again. If she warmed up on her Dynastars she would often feel unprepared or unsettled in the start because it was a ski you had to always be ahead of.
EDIT: Going back and thinking about her weight, if she is technically strong, I would look more at a 140-145 ski. She may overpower a 135 which would lead to double turning. The kids I've had on a 135 GS were closer to 50 lb. than 75. I had a U14 who is about your daughter's size and we put her on a 150. The shorter skis she would overpower and double turn.
