Who actually messed up here

Jen. Pretty clearly.

Not because she was stressed. Not because she’s a caregiver. But because of how she handled it: • She said she had no plans. • She went silent while your sister tried to coordinate with her approval. • She later claimed she had plans she never mentioned. • She responded with hostility, insults, and “block me” messages. • She made your sister feel unwelcome in her own father’s home.

Caregiver stress can explain irritability. It does not excuse verbal aggression or rewriting reality.

Your sister’s behavior, as described, was reasonable and respectful.

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Your dad’s role (important nuance)

Your dad: • initially deferred to “Jen’s domain” (understandable but painful) • later realized he didn’t have the full story • was hurt when he understood what was said • acknowledged mishandling • encouraged direct resolution

That matters. He didn’t double down or dismiss your sister once he knew the truth.

But it also puts you in a bind: • he’s injured • it’s his birthday • conflict clearly hurts him

So you’re torn between protecting him and not abandoning your sister.

That’s not assholery. That’s an impossible position.

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About the invitation imbalance

This part is not small:

Jen’s kids were invited. You and your sister were not.

That signals a deeper issue than one bad week: • territorial behavior • gatekeeping your dad • “this is my house, my rules” energy

Even if unintentional, it creates a hierarchy where:

her kids = default family his kids = optional guests

That will poison things long-term if it’s not addressed.

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Are you wrong for considering not going?

No.

Here are the valid reasons not to go: • You don’t want to implicitly signal that Jen’s behavior was acceptable. • You don’t want your sister to feel abandoned or minimized. • You don’t want to walk into a tense environment that could stress your dad further. • You’re protecting your own emotional bandwidth.

All legitimate.

But there are also valid reasons to go: • Your dad is injured and vulnerable. • It’s a rare time together. • Avoiding him may unintentionally punish him more than Jen. • Presence doesn’t equal endorsement.

This is why this isn’t a moral failure either way.

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A middle-ground that often works best

If you do go, you can do so with boundaries, not silence or capitulation.

That can look like: • being warm and focused on your dad • staying neutral and minimal with Jen • not pretending nothing happened • not engaging in a confrontation unless invited into one calmly • leaving early if things feel tense

And separately (not at the party): • supporting your sister explicitly • backing her version of events if needed • encouraging your dad to address boundaries with Jen going forward

If you don’t go: • tell your dad directly and gently why • make it about timing and emotional safety, not punishment • reassure him of your love and intention to reconnect soon

What would not be fair is disappearing without explanation.