You are definitely correct in wanting to change one thing at a time. You don't want to freak her out. ;-) I'm sorry to hear about your other dd.
Your reaction was completely understandable!
At her age, you should be trying PU/PD instead of pat/shh. She will still react negatively (she will cry, fuss, and wiggle) because you are trying to change her current habits, and this will confuse her. You shouldn't give up, though. Keep in mind that you ARE doing this for her benefit, and she needs to learn to sleep well. Make sure the read through the
Sleep Interview to get some idea about how to do this.
You will need to tackle her feeding to sleep first. You don't need to give her a pacifier. Let her try to find her own fingers. If she doesn't, that's fine, too. (My DS always hated the paci. As for his fingers, he chomps on those all day long but won't try to use them to sleep, so I just let him be.) You don't need to soothe her in order for her to fall asleep. By doing PU/PD, you are going to let her learn to soothe herself.
That should take a few days. Once that's behind you, you can work on extending naps by PU/PD (possibly in conjunction with pat/ssh, if she lets you).
HTH! Let us know if you have any other questions.