NTA for thinking it's unfair you can't have a drink under the circumstances you described (there's no partying or drinking problem). You're definitely not, and I think you should ask her what the issue is (is she scared you'll be tipsy in a foreign country and unable to help if she has an unexpected emergency? or is it jealousy that she can't drink?)

HOWEVER, you should still go on the trip together. Any trip without a child will be cheaper and easier to deal with and do what you two want to do together than a future trip with a child. That's not a "your life is over when you have a kid" mentality, it's just true that travel will be more challenging for the next few years until your kid gets a bit older than going on this trip will be now. So why not enjoy it together?