I have an LS and it's not a little BC. It is small compared to my HOG and the Manta I used to have but given the size of your friend, it might still be too big even adjusted down all the way. If they still made it, the LT Tech would be a great rig for someone that size. Only 25lbs of lift but for al80s or LP72s a great rig. I used to dive mine with LP85s in a drysuit.
However, if you find a good sidemount instructor, they may be able to loan or get ahold of one of a few models to try. Don't buy anything you can't get a chance to try on.
Another option is the Hollis Katana. It can be sized down. So can the razor and the XDeep. Though the X deep wing is on the large side for someone her size. I've built several of them for students and one guy was on the smaller side.
Expect to be cutting a lot of webbing and spending time moving plates, tri glides and tweaking the bands.
I've taught students using about 10 different systems and every one requires adjusting and tweaking to the individual. None fit right out of the box. Some have adjustable straps that can make fitting easier, but like a harness on a BPW, that can be a challenge. Those with a harness that you set and forget are fine but if swapping exposure protection all the time, they make take some getting used to.
The Nomad LS and Katana can be used with al80s and LP72s wet, and up to LP85s if diving dry. Plenty of lift.
Beware of people saying you can/can't do this with rigs unless they have actually tried them. You'll also get a lot of advice from those who have used one or two rigs and that's it.
Find an instructor that actually dives multiple rigs and has experience teaching people using multiple rigs. Not the one who took a one-weekend workshop to teach and seems to only recommend the rig they dive or their shop sells.
