The max depth is 18m/60ft, that's where you start. That's plenty deep enough IMO/IME for a new OW diver. After getting some experience, the limits should be pushed slowly. I've been certified for almost a year, and my two deepest dives are still 72 ft (probably the same wreck in the same current with the same stingrays
as your daughter). The whole point of an AOW seems to be an opportunity for an instructor to demonstrate how narced you can be and not realize it, hopefully they are also showing how fast you go through your tank and making sure you understand what options you may not have at 110' that were presented as viable at less than 60'.
OTOH, at age 12 kids are still growing like weeds, and we still don't understand how pressure affects bone growth. If it were my 12 year old (and I'm still a few years away from that stage) I'd probably want to limit him/her to 60ft. Not my call for your kids, obviously, just something to consider.