The Scenera is $69 at my wal-mart, so maybe worth pulling the box & price checking it to see what it actually is. Wal-mart isn't so good at changing prices sometimes...
Bolero is made by evenflo and harnesses to 47lbs.
If they have an alpha omega right now, why can't she use it? At 19mos I doubt that the little girl is too tall for the top usable harness height.
You might tell the mom that the shield booster she is using (if it's actually stickered to 30lbs,) was recalled due to the risk of young kids submarining. In Canada the lowest weight manufacturers are allowed to certify their boosters to is 40lbs. Some of those shield boosters also had a recall about the routing of the belt if it's a lap/shoulder belt.
You could also use an illustration as simple as telling mom that aside from her dd legally having to be harnessed still, boosters like that are as if someone took a plastic bar and held her own lapbelt 6" out from her abdomen. Imagine if she crashed and had to travel 6" at 50km/hr before impacting the seatbelt? Kids have died because of shield boosters... Manufacturers quit making them largely in part because of law suits.
But anyways, if she has an appropriate seat right now - which I'd be pretty sure that at the moment the AO is appropriate for her weight and size, just help mom get the seat installed.
Did you happen to ask mom why she moved her dd to a booster seat? Sometimes there are reasons that need to be addressed before parents are willing to make a change.