Morning E.-
Our dd showed signs at 18 mos, too. We got one chair to start (& gradually got one for every bathroom and now that she's almost 3 the potty chairs are gone and all of the toilets have the seat you can pop in sitting next to them).
I bought "The No-Cry Potty Training Solution" by Pantley and read it to have a little background just for us...I knew 18 mos was on the early end, so I didn't want to push, but still wanted to know we'd be stearing her in the right direction.
We let her come in with us and showed her how it all worked. Sometimes she'd sit on hers and sometimes she'd just be so curious about us...kind of creepy but I'm sure it helped.
Over the next two months, she'd come in with us and began to sit more often, so we made up songs and had a routine of sitting, reading her potty books and other faves, sing and hopefully pee or poo. If she did, we made up super silly dances that she loved. We even did these in public restrooms.
That reminds me...she grew obsessed with ALL toilets and asked all visitors to our house if she could come into the bathroom >:/
I remember after a few days of this taking her to buy any and all panties she wanted at Target-she was so excited. The first pack I'd bought were so boring to her. The new ones were 'hers.'
I bought a product called a piddle paddle for her carseat because I was worried about accidents when we were out. I never told her what it was, and for some reason she never asked? Made me feel better.
I began carrying an entire change of clothes down to shoes in my bag-never needed them!
Gradually she just started to want to go, so we made it official and every two hours I didn't ask her if she had to go, I just took her with me, as a routine. By a week or so of that (a bit exhausting but she could count on it and it made me sure she was empty) we were out of diapers for errands, playdates, for everything-panties all day!
By her second birthday, she was in panties all day, but diapers for nap and bedtime. We actually just last month began undies all the time, and it's been easy.
best of luck...the bottom line I think is to be completely supportive and prepared, but follow her time table and never push it.
Cheers!
J.