It can be VERY expensive to retrofit shoulder belts. I've seen it be as much as a grand for some cars. The 86Y or Kid-Y is a much better bet. I haven't priced the KID-Y but the 86Y was about $80 including shipping. It includes the heavy duty anchor bracket. If she is even somewhat mechanically inclined she can install the anchor herself using the generic tether location info found in the red tether manual. Depending on the car, there may be a predrilled hole (which she will have to drill out to make larger). She will also need a toque wrench to tighten the bolt for the anchor to the proper tension. Most guys with an interest in tools will have a torque wrench laying around somewhere. They are a common tool and fairly inexpensive ($10) so she can probably borrow one from someone she knows. If not, Kragen and Pepboys will usually let you use one to check something real quick if you ask nicely. ( works just like a regular wrench, except to turn a dial to the lbs of pressure you want, turn the bolt, when the wrench clicks, you are done). Note: she would also want to check if the booster her daughter has is compatible with the harness.
As for right now, I'd put the girl in the front with a booster.
As far as the ELR belts in the outboard rear, You can install a car seat using them. You use something called a belt shortening clip. It looks like a locking clip, only bigger and made from a steel alloy instead of nickel. You can order them from any Ford dealer for free. I've had them try to charge me for them, but if you insist the look it up, they are free. I get them literally by the case to use as locking clips for events. For that matter, if you private message me, I'll mail one out, along with step by step pictures of me using it. Some techs know how to use them still, but even when belt shortening clips were part of the curriculum there weren't that many who ever needed to use one IRL. I had a car that needed one until about 2 years ago, so I'm pretty sure I can still do it,
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If you can obtain a bsc maybe your friend could scrape together enough money for an Apex.
It sucks bigtime that latch laws forced Britax to stop making the Laptop.
Kimberly