You don't want the nose tucked in, you want to ride her into the bit. With a snaffle, pick up a soft feel of the horse's mouth, but don't do any more than that. Feel so light that you're almost holding hands, so to speak. Do lots of transitions, from gait to gait and within gaits, to help her get her hindquarters engaged, and get some forward motion and impulsion. If you can maintain that gentle "handshake" with her mouth through the transitions, riding from your seat, not your hands, she'll start seeking correct contact.
If you focus on tucking her head in, she'll fall behind the vertical, behind the bit. This is not good. She'll be heavy on her forehand, prone to hollowing through the back, and tense. Unfortunately, just messing with the horse's face can get something that can look like proper collection, and even fool some judges, but isn't a correct or even comfortable posture for the horse, and can even cause problems down the road. Falling behind the bit is tantamount to an evasion. The horse is trying to avoid the moving bit and get away from it, not seeking out the contact willingly in partnership with her rider.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown