Thank you for your query. Travelling with children can be very daunting. But worry not, many mothers manage to do it time and time again.
Even at 3 months old your child will pick up on changes and notice that they are not in their usual environment. It is therefore important to keep things as familiar as possible. Use the same stroller, child carrier, bottles etc. If you have to buy new ones,, let them spend some time getting familiar with them before the flight. Bring a pillow or jumper she is familiar with. Carry as much milk as she will normally consume during the period of travel and try and keep her feeding, sleeping and changing routine as normal as possible.
It is unpredictable which children will react to changes in cabin pressure. But nursing her with milk or water or allowing her to suck on a pacifier during take off and descent will keep her doing a swallowing motion that will relieve any uncomfortable sensation in the ears.
It is not advisable to give your baby any medication to sedate her during the flight. This can be dangerous and cause unwanted side effects in a very isolated environment. Travel with some pediatric paracetamol
(within the guidelines of the airline) and any medication your baby normally takes on a daily basis. Also take plenty of diapers and a change of clothes.
I am sure the airline will be able to advise you on the best seat for you and whether you need to block of any other seats on your row.
All the best, this is the best age to travel with children. At least she is not a mischievous toddler yet!
Wishing you a safe trip,