TL;DR You can't make her view herself in a particular way, you can only encourage it.
If and when therapy comes up, promote it or stick in a short plug, but don't be too annoying. This is a larger problem than you should be trying to address. What follows is an approach to help her help herself, but it should in no way be treated as a substitute for therapy.
By "help someone" you really mean "change someone". Let's be clear that this particular change is personal, and you are not that person.
The first step is to protect yourself. Accept it's ultimately up to her to change. Be careful not to have hopes or expectations of this working out in any particular way. If you can manage your hopes and expectations about this, you can proceed.
If you cannot manage yourself, if you become or think you'll become too invested, then do not take this on. Doing so runs the risk of damaging the relationship.
(From what I can tell, it's safe for OP to skip this step. I'm including it for completeness.)
If your friend doesn't talk about this, then the first step is to start the discussion. When the behavior comes up, try to talk about it. Depending on the behavior, you may be able to talk about it while it is active; alternatively, it should always be safest to talk about it afterwards when they've had time to cool/normalize.
The goal here is to simply open up territory for future discussion. Ask about the behavior, the trigger, the feelings, her feelings towards it—whatever is easy, safe, or convenient to talk about.
Your friend retains the right to stop the probe at any point: from before you even start to mid-sentence, it's all fair game. This can be frustrating; expect it. You may need to probe (gently) at the same thing multiple times. You may not get anywhere. Remember, change is their choice. You volunteered your time and effort to go down this route—don't expect a return on your investment.
Confirming can and should be done as you probe. Whereas the goal of probing is to open up territory, the goal of confirming is exploring the same territory.
Your friend has a different opinion of herself. You need to acknowledge that and understand it. Echoing is appropriate. This is an issue with her relationship to herself. She might not truly understand the basis of her opinion, and this steps serves to bring the logic—whatever it may be—to light.
Warning: Before you proceed with Identify, your friend should be in a level-headed state. Some people aren't interested in being level-headed, so you might not get to this step. If your friend stops being level-headed, don't try to push through. Wait for the next opportunity.
There are zero or more contradictions in your friend's logic. You need to identify them. In fact you may need to take a break after confirming to really analyze and think it through.
There may be zero contradictions; it is possible. This means there's a difference in assumptions or values. Do not assume/impose your own values or assumptions. You may need to go back and confirm her underlying assumptions and/or values.
If this is the case, you may be done. You can discuss the values backing her logic, but you must respect her values. You can try to repeat this approach for one or more values. The same warnings and precautions apply. Warning: Success with an underlying value does not correspond with direct success in changing a behavior, so don't expect it to.
If there is a contradiction, bring it to her attention. She may not see it as a contradiction. Strive to understand her point of view. Again: Do not assume/impose your own values or assumptions. You can compare with your own view, but hers trumps. Reevaluate whether there are any contradictions.
Warning: Your involvement may end here. The rest of the steps need to be driven by your friend. She may involve you, but understand that she should be the driver, not you. I include the next steps for completeness.
This step is personal. Going through the prior steps hopefully incites your friend to take this step. I cover this for completeness, but also because these steps can be self-administered in which case the hope is that you will reach this step.
You should now have a solid understanding of the why driving the behavior. You may have instigated the investigation, or a concerned friend may have led you to this point. At this point there's one question you should answer:
Should I change?
Make sure you answer the right question. "Should I change?" is different from "Do I want to change?" We're seeking to align our self with our core values. This can be difficult. Allow yourself time to think through and process it. Try to avoid shelving the question. This may be appropriate, but it's not appropriate as a habit.
Ideally the answer is "no". "No" is an acceptable answer. In this case it means your behaviors are already be in line with your values.
The alternative is "yes". If this is the case, you've got a lot of planning to do.
Whether the answer is yes or no, you should plan. You went through a lot of effort to get to this point, you should now fortify your position.
Examine your relationships. These will either erode or support your position. There is no middle ground. Not being supportive signals your position is unimportant, and this does have a long-term impact, so weigh it appropriately.
If your answer was yes, then you need to maintain a focus on this change and applying it to your daily life for an extended period of time. Some people or changes can be quick, but it's best to assume this is not you. There are many resources on making changes, and I encourage you to seek them out.
Note: Success (with making a change) is a road often littered with failure, something we'd expect the OP's friend to struggle with more than most. It's a bit ironic. Mentally prepare for and accept failure.