Oh mama, you're not a failure!!! A few things might be happening...
First of all, was it the same scale as last week? Scales can differ by a few ounces, and really, 3 ounces isn't much at all!!
Did she just poop? One good squirt can weigh a few ounces, so if she hadn't pooped last week, and did poop right before being weighed this week, that could be a difference!
What about eating? Last week had she just eaten before being weighed? This week had it been an hour or two (or three even?) Because that can change a weight, too!!
Now all of that aside, some babies take a little longer to get back to birth weight, and that can be normal. How's her output? Is she peeing? Is she pooping mustard-looking poop? Is it green at all? Green poop can be a sign of a foremilk/hindmilk imbalance. Not enough poops or pees in a day could be a sign that she's not taking in enough. NONE OF THIS IS YOUR FAULT!!! It takes a while to get into the groove of the breastfeeding relationship!!!
Try the teas, they can't hurt any. Pay attention to your diet, are you eating? (it can be easy to forget to eat!) Are you drinking to thirst? Don't push too much fluids, there's no need to drink 100 oz a day, just drink to thirst. You can also try pumping after she feeds, see if you get much. If you do, and if it's watery-looking, then she's not staying on long enough to get hind milk. So work on waking her...when she comes off, change her diaper and play with her a little, then put her back on the same breast again. If she stops sucking, tickle her feet, play with her chin, see if you can get her interested in sucking again.
My second took 4 weeks to get back to birthweight, then was an incredibly slow gainer after that, but he had some serious health issues that complicated things. It's unlikely that your little one has anything "wrong" with her, but do pay attention to her, how she sucks/swallows, how she breathes, whether she has alert periods from time to time, etc.
Most of all, just relax, and enjoy your baby! I udnerstand how you're feeling, I sat awake at night crying trying to feed my second, the feeling of failure was horrible, HORRIBLE!! Especially since my first had been such a great feeder, so robust, so healthy, hit every milestone way early...then to have a failure to thrive baby made me think that something was wrong with me!!! But we eventually figured it out...his drs said there was no way he'd be able to feed at the breast, but he did!! And your daughter will continue to, too!!