I am excited to hear you both are a having a happy relationship ;D
I am just a teenager but I would suggest you to propose her according to her style. Does she like classical? or the modern way?
If she like it in the classic way, I suggest you to bring her to a fine dinning. The disadvantage of this classical way, sometimes it seems to be not so special and surprise because it's been done in many possible ways.
When it comes to modern way, this where all the most trending way used. For example, making ur proposal in a public place where people usually will right away record and make it 'viral'.
Both has it's pros and cons because even as a teenager, I like it in classic way than making it so modern-ish cause I don't want my boyfriend to trouble himself so much and I still find it romantic. (If only I have a boyfriend (: ... )
I hope this can help you! Wish you a very much good luck and hope I can hear the good news! <3