I would recommend start by introducing 'hot words' at home as soon as you bring her home such as sit, stay and down so she gets used to the fact that certain words mean i do an action and i get a reward. When going to classes I recommend starting with the beginners obedience classes and then if you want move on to advanced but obviously speak to someone at your local club and ask on their advice because everyone has different opinons. Because westies are smaller dogs they grow up quicker than larger dogs so they will probably be physically mature before 18 months but i would hold off on agility until at least 12-18 months. Agility definately supports obedience because once theyve learnt the basics of obedience and being off the lead they have to
listen to be quick- they need to be at your heel, they need to follow you do as you say and get round fast, obviously like everything else it comes with time and the key principal is to keep things FUN fun fun fun

. Don't forget to consider other classes such as clicker (you can also start this at home) and heelwork to music

. Westies can be lovely little dogs and agility is a great way to keep them fit, I dont know how savvy you are with the breed but just watch that they can be prone to skin diseases and eye problems (maybe associated with being such a pale colour) and they appreciate a bit of non-toxic suncream on their pinkest bits (noses, ears etc) in the hottest sun

Sorry if i've gone off on one haha and I hope that helps, I'm a bit of an animal nerd so if you ever need an opnion (not a replacement for veterinary advice

) don't hesitate to give me a shout xx