I'd try night weaning first as you'll probably get the greatest benefit in terms of rest from it! We did the Dr Jay Gordon plan with DS1 and it worked very well:
drjaygordon.com/attachment/sleeppattern.html
I'd also maybe try the occasional "daddy bedtime" while you go out somewhere to get her used to going to bed without milk. Once we did that with DS1 I ended up feeding him morning and evening for another year because it was so much easier - I was getting sleep, didn't have to worry about bedtimes, could go away (once I had pump), etc. etc. Obviously you don't need to do that, but just to show what a difference just those steps made.
Re need for milk, DS2 never really drank milk of any sort after he weaned. He drank plenty of water and ate lots of other dairy (cheese, yoghurt) and other calcium sources (baked beans, etc.), so I didn't worry about it. Toddlers don't actually need cow's milk, it's just a useful source of particular nutrients.
Finally, around 17/18 months is a tough time anyway as a lot of babies have a big growth/developmental spurt around then, so you may find it's a lot easier to night wean once she's through it (or she may just start sleeping through by herself - DS2 did, excellent baby!).