Here's what Dr. Sears says in The Discipline Book:
Motivators-Distractors
Point out sore thumb. Compare sore with other thumb. Show 'buck' teeth in mirror. Run fingers over protruding teeth. Busy bored hands.
Relaxers
Play soothing music, have cuddle time, read together (child holds book)
Subs
[Teach your child to] 'Hide thumb' by making a fist, squeeze thumb, suck tongue.
Special Help
Dental appliance, distasteful reminders - paint-on products, Band-Aid, tape, tongue-blade splint, wear mittens.
I think that while these might seem less effective at first because they are less severe than things like hot sauce and slapping her hand, they might actually be more effective because thumb-sucking is, besides a habit, a comfort thing. So adding stress around it will only make it harder for her to stop.
I really like the "hide thumb in fist, suck on tongue" trick because that way she can start to do it around her friends when she feels stressed or would otherwise want to suck her thumb, but doesn't want to because she fears teasing. Teaching her this trick puts you on her side. She will be more willing to work with you on ending the habit. It also gives her a transition technique.
I think the cuddle time, book reading, etc. will be more effective, too, if you can make this a project you two do together, as in, "Brooke, come to me when you feel like sucking your thumb, and we'll do something togehter."
Good luck.
L.