I took a trip abroad with my mom 2 months after giving birth. am I actually insane??

okay so this is long but please bear with me because I genuinely need outside opinions on this.

I'm a first-time mom, early 30s. and last year when I found out I was pregnant, I made a plan.

my mom was turning 60 this year. she also just retired after 30+ years of teaching. so I asked her, hey, what do you actually WANT to do to celebrate? and she said, quietly, "I just want to travel somewhere, just the two of us."

I'm not exaggerating when I say that hit different. we have never once traveled alone together. and I didn't even know that was her dream until that moment. she spent her whole life working and raising us and that was the ONE thing she wanted.

but I was already pregnant. and I knew once the baby got older and actually recognized me, leaving would be so much harder. my older sister already has two kids and she basically stopped doing anything for herself after. so I started thinking, what if we go before the baby hits 100 days? before they really lock onto you as mom? and I talked it through with both families AND my husband.

everyone was on board. like, genuinely supportive. my husband is actually better with the baby than I am (I'm not joking), so the plan was: I go with my mom, husband takes paternity leave, MIL comes to help, baby has 100% adult supervision at all times. we even arranged it so that if ANYTHING happened to the baby we'd cancel or come back immediately.

(side note: while I was 8 months pregnant, my husband and his mom did their OWN trip to eastern Europe together. I stayed at my parents' place and was totally fine. so this was kind of a both-families thing.)

baby arrived naturally at 40 weeks and 3 days, totally healthy. currently 50 days old as of when I planned the trip, about a month before we'd leave.

and then.

my older sister called our parents over and just. unloaded.

she said, and I quote:

"how can a mother leave her newborn to go on a vacation abroad. this is socially embarrassing and completely abnormal. and it's even worse that grandma is the one LEADING this instead of stopping it. your image is completely ruined. I asked people around me and everyone thinks you're both insane. only people with no family or values would do something like this. I have to be the one to stop this because I'm family. [my name] is immature and mom is just enabling her instead of correcting her. is THIS how you raised us."

she said ALL of that. to my mom. in front of my dad.

my dad got so mad he snapped at her and left. and my mom just sat there, completely blindsided, and went quiet and said "...I won't go then."

and now my mom can barely pick up my sister's calls. she's that hurt. she was SO excited about this trip. we planned every detail together. she was GLOWING. and my sister just walked in and torched all of it.

here's what's making me crazy though: my sister didn't come to me. she didn't call me, didn't text me, didn't say a single word to me directly. she went straight to my MOM and ambushed her. and now she's doubling down, saying "my opinion won't change" and calling it "mom's selfishness" and "she can't even give up one little trip."

so I'm asking here, genuinely. is what I'm doing actually that insane? like obviously if you hear "mom left newborn for vacation" with zero context it sounds bad. but the baby is not being left alone. dad is there. grandmother is there. everyone agreed. everyone is present.

and my mom spent 30 years giving everything to her students and her family and this was supposed to be HERS.

do you think we're actually being immature and selfish? and was my sister's approach okay, as a family member?