I believe a healthy relationship requires trust, respect and honesty, and the three walk hand in hand. I certainly understand you being concerned when you feel your partner has not been honest and upfront.
I also think one needs to look at things both from the microcosm and the macrocosm. We should consider every incident on it's own merit as a singular event while also considering patterns of similar incidents.
As a singular event, yes a form of dishonesty occurred, but it requires an understanding of the complexities of personal dynamics, external influences and relationship dynamics.
Personal dynamics include all of the psychological baggage we carry throughout our lives, including our accumulated wounds and their effect on our behaviour, like our ability to trust and our desire to avoid further wounds.
You both have had unique experiences, both positive and negative, that have shaped your respective perceptions, thoughts and behaviours.
For example, your partner may have developed a pattern in childhood of hiding certain bahaviour in order to avoid being judged and rejected by a parent. She therfore needs to hide from you both the fact that she failed at quitting and her smoking, lest she suffer your judgment or rejection.
You, on the other hand, might have some wound associated with honesty and react to dishonesty in a disproportionate way.
External influences can involve, in this case, the social conditioning one receives about smoking as well as the effect smoking has on a person, as they relate to personal dynamics. Most smokers today have developed beliefs that smoking is evil; that it both kills smokers and those around them, that it is highly addictive, and that one needs to hide it from society. Long before your relation with this person, she had already been conditioned to hide her smoking, to lie about it, since it is allegedly a sin against humanity and the environment and those who smoke must have something wrong with them and should be separated from society.
Smoking is also pleasurable, has several health benefits, enhances intellectual abilities and contains chemicals that can be highly addictive. All of these attributes provide incredibly potent reinforcements to continue smoking.
So there are powerful forces at play upon the smoker, both to make them want to quit and to want to smoke. An even greater schism can form when we connect these forces to personal dynamics, including, for example, one's fear of rejection on one hand and one's desire to nurture (or gratify) one's self on the other hand.
The relationship dynamics combine both individual's personal dynamics as well as the effects of external influences as they relate to the respective individual's personal dynamics.
Although you both have had access to the same social conditioning, the effect will be different due to several factors, including the fact that one of you have received the conditioning as a smoker and have had the threat of societal rejection looming over their head and the other has rarely been afforded the opportunity to empathize with the former's experience as a smoker.
One often needs to trust in order to be honest. A smoker learns early on that they cannot trust society to treat them fairly and to not reject them, and therefore, cannot easily separate a partner's distaste for smoking from society's distaste. The fears of society's judgment and rejection is easily transferred onto the relationship.
So, from a microcosmic view, as a singular event, this issue of honesty is complex and should initially be viewed in light of several considerations, including the aforementioned.
However, from the macrocosmic view, if there are other instances of dishonest behaviour, you would also need to take them into consideration after initially viewing them on their own merits and assigning them certain values.
As I mentioned in an earlier comment, there are several forms of dishonesty, some of which are both understandable and forgivable and some which are so dangerous to a relationship that they should provide a giant red flag, accompanied by a trumpet blowing the signal to retreat.
For example, you are choosing to be dishonest, through omission, by not telling your partner your current thoughts and feelings during this difficult time in hers and her family's lives. Yet this form of dishonesty doesn't seem to register with you as dishonesty and, if it did, probably wouldn't be assigned the same value as your partner's choice to hide her smoking from you.
Although it seems to me that you are overreacting to her trying to hide her failure to quite from you, if there are patterns of dishonest behaviour, or other childish ways she handles being confronted with her behaviour, then these need to be taken into consideration and your reaction would be more understandable.
Just make sure you are reacting to the right thing and the other person knows what you are reacting to.
From a personal development perspective, perhaps there's something for you to learn about yourself from your reactions. You seem to be hanging onto the honesty aspect, as if she had hurt you with her dishonesty. It might be beneficial for you to work backward through your life to your early childhood and review times when people had been dishonest with you and how you felt.
Perhaps the concept of honesty got hammered into you in a very specific and painful way when you were young and, although you are reacting to your partner's perceived dishonesty, you are actually replaying a scenario from your childhood and the pain you feel from your partner's behaviour merely echoes an earlier wound.
I apologize for the length if this post but I thought it could be beneficial to break things down the way I did and I could find a briefer way of doing it.
Gonzo