Hi M.:
First and most important,do not make the mistake of (issuing punishment)for thumb sucking.Most older children that continue to suck their thumb are suffering from some type of stress,boredom,or frustration. Punishing them will simply escalate the problem.The most important thing you could do, is attempt to find out exactly what her insecurities are,and help her to resolve them. Dr Benjamin Spock,says that in the older child,where thumb sucking has become an empty habit ,that parents are urged to calmly remind them when they begin doing it. Other cures involve bitter liquids applied to the thumb.The Dr also cautions parents against using restraints as such devices,only frustrate the child more.In all cases,children require emotional support.I don't know what guard you used previously,but there is one ,called the (thumbbusters) which a father developed,for his daughters who all were thumb suckers.You can find it on line. I hope this helped a little M.. The most sound advice I could give you, is talk to your daughter privately,and try to find out what her insecurities are,and let her know, that you want to help her,so she doesn't have alot of problems later with her teeth.If its as simple as (bordom) maybe you both could find something to busy her hands.I wish you and your darlin daughter the best.