It can take up to three weeks for a baby to regain their birthweight, though two weeks is more typical.
If I were you, I would make an appointment with an IBCLC. I wouldn't go another two weeks. If there is a problem (latch, milk supply, etc) it is much better to catch it and work on it sooner rather than later.
How often does she nurse? Very often a laid-back baby needs to be reminded to nurse frequently. She should nurse a minimum of 8-12 times in a 24 period. And honestly, I would suggest more often if she is not gaining weight at this point. Do your breasts feel full? And do you think she is trasferring milk effectively? Your breasts should feel softer when she is done.