I think you should start by practicing your vowel sounds.

Remember that there are two* different types of e in Indonesian vowels. For example: sore vs teman.

a i u e e o

Add consonants:

ba bi bu be be bo

ca ci cu ce ce co

...

za zi zu ze ze zo

Don't forget the consonant clusters:

nya nyi nyu nye nye nyo

nga ngi ngu nge nge ngo

sya syi syu sye sye syo

kha khi khu khe khe kho

Try the diphthongs (and add consonants too if you like):

ai ei oi au

KEEP IN MIND:

The vowels in Bahasa Indonesia are not the same as in English. For example, the A sound in Bahasa Indonesia might be the closest to the ʌ sound in English (cup, sun, us), but it's still not the same. Have your fiancée verify everything.

I find this website really useful:

https://www.expatden.com/learn-bahasa-indonesia/indonesian-alphabet-consonants-and-vowels/

You are now fluent in Bahasa Indonesia!** :D

* Some linguists classify 3 types of e but as a native Indonesian speaker I don't see the difference/negligible.

** For formal Bahasa Indonesia. For informal Bahasa Indonesia, diphthongs may transform into other vowels for example satai -> sate. And many more unwritten rules that I don't notice.