Baby cereal in bottle? 4 months

I’m flying a 12 hour flight alone with my baby in 2 weeks, she will be exactly 4 months (and 3 days).

My MIL recommended adding some baby cereal to her bottle for the flight so she will be more full and hopefully sleep longer during the flight.

I’ve read that it’s recommended to wait till 6 months but on the package it says 4 months and I’m confused.

Obviously if it will cause issues for baby, I’d rather not add, but if it’s ok I’d be happy to.

What are your thoughts ??

Also- I do NOT plan on making this a regular habit until later on. It would be just for the flight so it will keep her full a little longer.