I don't think she's being hypocritical, certainly don't think she deserved it 
I simply cannot understand this perspective. The concept of hypocrisy seems to perfectly align with this situation, if the stated premise is correct.
One simple definition of hypocrisy is acting in a way that goes against your stated beliefs.
If you are publicly stating it's bad to cheat and painful to be cheated on—then proceeding to cheat yourself is an act that directly contradicts your stated moral position. This contradiction is the very essence of hypocrisy. It means setting a moral standard for others or for the relationship that you are unwilling or unable to meet yourself. The act of infidelity itself, especially following strong public condemnation of infidelity, forms a clear, logical link to the definition of hypocrisy because it reveals a double standard.
Now, I don't know the ins and outs here and quite frankly haven't got the sustained interest to delve deeper, but if she cheated and is now throwing a pity party because she's being cheated on, I simply can't figure an alternative definition for that behavior other than hypocrisy. Her current distress over being betrayed would be seen as disingenuous or entirely self-focused, as she had previously inflicted the very same pain on another person. The pain she feels now highlights the very wrongness she previously dismissed, making her current victim status a classic example of situational irony rooted in her own hypocrisy.
and being betrayed by infidelity doesn't fucking benefit anyone, ever, in any way, shape or form.
Again, I must disagree here. I can't speak to what anyone deserves, though personally, I lean toward a philosophy of reciprocal morality or "an eye for an eye" in this specific context. We've all seen bullies get stood up to and get a taste of their own medicine. In my perspective, this kind of direct, lived experience is often the single most effective way to address bullying behavior. My brother in-law, a PhD for that matter, has an idiom that I've always liked. He says as unenlightened and barbaric it may seem, some people just need a smack. I do believe this is true. It frequently humbles the person and forces them to re-evaluate their actions before inflicting pain on another. The benefit, in this difficult situation, is the potential for a powerful and lasting lesson learned through consequence.
Surely the same is true here? If a cheater feels the pain of being cheated on—the betrayal, the loss of trust, the deep emotional trauma—they might think twice before enacting such a betrayal again. The experience could force them to genuinely connect their actions with the profound, negative consequences they have now personally suffered. The "smack" in this analogy is the emotional shock of betrayal, a visceral consequence that cuts through abstract moralizing. While it's a terrible, painful benefit, the lesson learned through direct experience of the consequences is often a more effective deterrent against future bad behavior than simple ethical instruction or moralizing. This difficult lesson could lead to profound personal growth and ethical clarity, ultimately benefiting their future relationships by instilling a deeper empathy for the pain they previously caused. 
I suppose the counter argument could be that it normalizes cheating. It could potentially lead to a mind set of: '... well everyone cheats I suppose' but I can't imagine this is the normal response. Most people I know who were cheated on become incredibly anti-cheating. Admittedly that is just my experience. It does seem to be reflected on forums such as this though.  
Irrespective I don't believe sympathy is warranted and can't begin to understand the argument that it might be. Look at this situation in any other context, would you have sympathy? Suppose I'm a scammer, stealing money from retirement funds from old people over the phone. Suppose I then grow old and fall victim to the scam? Do you really feel bad for me? 
If I'm a thief and rob someone's house on Christmas eve, suppose I then get robbed on Christmas day... etc etc
 [This message edited by DRSOOLERS at 9:30 AM, Friday, October 31st]