のパーティーには

to [someone's] party

→ の
phrase Rare #23,958
to [someone's] party の marks possession, as in "someone's party." に indicates the destination or setting, while は adds emphasis or contrast, roughly "as for [someone's] party."
JA: 妹のパーティーには友達がたくさん来た。
EN: A lot of friends came to my sister's party.

彼女は今夜のパーティーには来ないかもしれない

She might not come to the party tonight.

トムのパーティーには招待されなかったんだ

I wasn't invited to Tom's party.

彼は夕べのパーティーには現れなかった

He didn't show up at the party last night.

残念ながらあなたのパーティーには出席できません

Unfortunately, I can't attend your party.

今夜のパーティーには行きますか

Are you going to the party tonight?

もし私の家大邸宅だったら私の誕生日のパーティーには知人みんな招待するのだが

If my house were a mansion, I would invite all my acquaintances to my birthday party.

トムのパーティーには行きたくないってこと

Are you saying you don't want to go to Tom's party?