it's all well and good ignoring grumbling, but unless you teach her new coping skills, this isn't going to stop her doing it.
I agree with Karma. You have not been given the correct advice by the behaviourist. You need to train a good strong "look at me" for times when her behaviour to the doorbell, others, other dogs, noises etc is unacceptable to you.
You also need to rethink the grumbling - don't ignore it - distract her with something she really can't resist (perhaps a favourite toy since she's not food orientated?). Then use the "look at me" and reward her when she does it right.
Baby steps at first, don't expect it to change overnight.
Develop your voice to command, don't waiver. Deep, strong, solid voice for commands, higher, squeaky, excited "Good girl" for reward. Above all be consistent in your training. Your voice is very important for giving your dog a sense of security (even if we don't feel very confident ourselves!!
)
Fearful dogs lack self confidence, they look to us to provide them with security. Is your lack of confidence with her perhaps influencing her behaviour?
You CAN do this you know.