Suvi is a character that you won't be able to take to the battlefield - she is one of the Tempest crewmates. However, she, as a romance option, is only available to the female character, Sara Ryder - while playing as Scott you won't be able to flirt with him and the relationship will be limited to friendship. Suvi Anwar is a character you can have close relations with - by engaging in that relationship you won't be able to flirt and romance with other characters. You can flirt with her each time you finish a main mission (Priority Ops).
Note - before engaging in a close relationship you can save the game. Afterwards, you can go through the rest of the romance, load the saved game and engage into a relationship with a completely different character. The option to romance other characters is locked only when you are engaged in a close relationship with somebody.
Below you can find a table presenting all of Suvi's loyalty missions, coupled with the requirements that must be met to unlock them. Detailed description of every single one of them can be found in "Allies and relationships" section of this guide.
How to unlock
Suvi Anwar: New Discoveries
Being in a relationship with Suvi.
Note: the option to engage in a close relationship will appear during "Hunting the Archon" main mission, provided that you've flirted with her before that point. Remember that this choice will prevent you from flirting and romancing other characters. If you still want to romance with others and at the same time see the final parts the romance with Suvi, save the game before starting the conversation with Suvi and load it later if needed.